OCFS2 1.2 - FREQUENTLY ASKED QUESTIONS

OCFS2 1.2 - FREQUENTLY ASKED QUESTIONS

    GENERAL

  1. How do I get started?
  2. How do I know the version number running?
    	# cat /proc/fs/ocfs2/version
    	OCFS2 1.2.1 Fri Apr 21 13:51:24 PDT 2006 (build bd2f25ba0af9677db3572e3ccd92f739)
    
  3. How do I configure my system to auto-reboot after a panic?
    To auto-reboot system 60 secs after a panic, do:
    	# echo 60 > /proc/sys/kernel/panic
    
    To enable the above on every reboot, add the following to /etc/sysctl.conf:
    	kernel.panic = 60
    

    DOWNLOAD AND INSTALL

  4. Where do I get the packages from?
    For Oracle Enterprise Linux 4 and 5, use the up2date command as follows:
    	# up2date --install ocfs2-tools ocfs2console
    	# up2date --install ocfs2-`uname -r`
    
    For Novell's SLES9, use yast to upgrade to the latest SP3 kernel to get the required modules installed. Also, install the ocfs2-tools and ocfs2console packages.
    For Novell's SLES10, install ocfs2-tools and ocfs2console packages. For Red Hat's RHEL4 and RHEL5, download and install the appropriate module package and the two tools packages, ocfs2-tools and ocfs2console. Appropriate module refers to one matching the kernel version, flavor and architecture. Flavor refers to smp, hugemem, etc.
  5. What are the latest versions of the OCFS2 packages?
    The latest module package version is 1.2.9-1 for both Enterprise Linux 4 and 5.
    The latest tools/console package version is 1.2.7-1 for both Enterprise Linux 4 and 5.
  6. How do I interpret the package name ocfs2-2.6.9-22.0.1.ELsmp-1.2.1-1.i686.rpm?
    The package name is comprised of multiple parts separated by '-'.
  7. How do I know which package to install on my box?
    After one identifies the package name and version to install, one still needs to determine the kernel version, flavor and architecture.
    To know the kernel version and flavor, do:
    	# uname -r
    	2.6.9-22.0.1.ELsmp
    
    To know the architecture, do:
    	# rpm -qf /boot/vmlinuz-`uname -r` --queryformat "%{ARCH}\n"
    	i686
    
  8. Why can't I use uname -p to determine the kernel architecture?
    uname -p does not always provide the exact kernel architecture. Case in point the RHEL3 kernels on x86_64. Even though Red Hat has two different kernel architectures available for this port, ia32e and x86_64, uname -p identifies both as the generic x86_64.
  9. How do I install the rpms?
    First install the tools and console packages:
    	# rpm -Uvh ocfs2-tools-1.2.1-1.i386.rpm ocfs2console-1.2.1-1.i386.rpm
    
    Then install the appropriate kernel module package:
    	# rpm -Uvh ocfs2-2.6.9-22.0.1.ELsmp-1.2.1-1.i686.rpm
    
  10. Do I need to install the console?
    No, the console is not required but recommended for ease-of-use.
  11. What are the dependencies for installing ocfs2console?
    ocfs2console requires e2fsprogs, glib2 2.2.3 or later, vte 0.11.10 or later, pygtk2 (RHEL4) or python-gtk (SLES9) 1.99.16 or later, python 2.3 or later and ocfs2-tools.
  12. What modules are installed with the OCFS2 1.2 package?
    The kernel shipped alongwith Enterprise Linux 5 includes configfs.ko and debugfs.ko.
  13. What tools are installed with the ocfs2-tools 1.2 package?
  14. What is debugfs and is it related to debugfs.ocfs2?
    debugfs is an in-memory filesystem developed by Greg Kroah-Hartman. It is useful for debugging as it allows kernel space to easily export data to userspace. It is currently being used by OCFS2 to dump the list of filesystem locks and could be used for more in the future. It is bundled with OCFS2 as the various distributions are currently not bundling it. While debugfs and debugfs.ocfs2 are unrelated in general, the latter is used as the front-end for the debugging info provided by the former. For example, refer to the troubleshooting section.

    CONFIGURE

  15. How do I populate /etc/ocfs2/cluster.conf?
    If you have installed the console, use it to create this configuration file. For details, refer to the user's guide. If you do not have the console installed, check the Appendix in the User's guide for a sample cluster.conf and the details of all the components. Do not forget to copy this file to all the nodes in the cluster. If you ever edit this file on any node, ensure the other nodes are updated as well.
  16. Should the IP interconnect be public or private?
    Using a private interconnect is recommended. While OCFS2 does not take much bandwidth, it does require the nodes to be alive on the network and sends regular keepalive packets to ensure that they are. To avoid a network delay being interpreted as a node disappearing on the net which could lead to a node-self-fencing, a private interconnect is recommended. One could use the same interconnect for Oracle RAC and OCFS2.
  17. What should the node name be and should it be related to the IP address?
    The node name needs to match the hostname. The IP address need not be the one associated with that hostname. As in, any valid IP address on that node can be used. OCFS2 will not attempt to match the node name (hostname) with the specified IP address.
  18. How do I modify the IP address, port or any other information specified in cluster.conf?
    While one can use ocfs2console to add nodes dynamically to a running cluster, any other modifications require the cluster to be offlined. Stop the cluster on all nodes, edit /etc/ocfs2/cluster.conf on one and copy to the rest, and restart the cluster on all nodes. Always ensure that cluster.conf is the same on all the nodes in the cluster.
  19. How do I add a new node to an online cluster?
    You can use the console to add a new node. However, you will need to explicitly add the new node on all the online nodes. That is, adding on one node and propagating to the other nodes is not sufficient. If the operation fails, it will most likely be due to bug#741. In that case, you can use the o2cb_ctl utility on all online nodes as follows:
    	# o2cb_ctl -C -i -n NODENAME -t node -a number=NODENUM -a ip_address=IPADDR -a ip_port=IPPORT -a cluster=CLUSTERNAME
    
    Ensure the node is added both in /etc/ocfs2/cluster.conf and in /config/cluster/CLUSTERNAME/node on all online nodes. You can then simply copy the cluster.conf to the new (still offline) node as well as other offline nodes. At the end, ensure that cluster.conf is consistent on all the nodes.
  20. How do I add a new node to an offline cluster?
    You can either use the console or use o2cb_ctl or simply hand edit cluster.conf. Then either use the console to propagate it to all nodes or hand copy using scp or any other tool. The o2cb_ctl command to do the same is:
            # o2cb_ctl -C -n NODENAME -t node -a number=NODENUM -a ip_address=IPADDR -a ip_port=IPPORT -a cluster=CLUSTERNAME
    
    Notice the "-i" argument is not required as the cluster is not online.

    O2CB CLUSTER SERVICE

  21. How do I configure the cluster service?
    	# /etc/init.d/o2cb configure
    
    Enter 'y' if you want the service to load on boot, the name of the cluster (as listed in /etc/ocfs2/cluster.conf) and the cluster timeouts.
  22. How do I start the cluster service?
    If you have configured the cluster to load on boot, you could combine the two as follows:
    	# /etc/init.d/o2cb start [cluster_name]
    
    The cluster name is not required if you have specified the name during configuration.
  23. How do I stop the cluster service?
    If you have configured the cluster to load on boot, you could combine the two as follows:
    	# /etc/init.d/o2cb stop [cluster_name]
    
    The cluster name is not required if you have specified the name during configuration.
  24. How can I learn the status of the cluster?
    To learn the status of the cluster, do:
    	# /etc/init.d/o2cb status
    
  25. I am unable to get the cluster online. What could be wrong?
    Check whether the node name in the cluster.conf exactly matches the hostname. One of the nodes in the cluster.conf need to be in the cluster for the cluster to be online.

    FORMAT

  26. Should I partition a disk before formatting?
    Yes, partitioning is recommended even if one is planning to use the entire disk for ocfs2. Apart from the fact that partitioned disks are less likely to be "reused" by mistake, some features like mount-by-label only work with partitioned volumes.
    Use fdisk or parted or any other tool for the task.
  27. How do I format a volume?
    You could either use the console or use mkfs.ocfs2 directly to format the volume. For console, refer to the user's guide.
    	# mkfs.ocfs2 -L "oracle_home" /dev/sdX
    
    The above formats the volume with default block and cluster sizes, which are computed based upon the size of the volume.
    	# mkfs.ocfs2 -b 4k -C 4k -L "oracle_home" -N 8 /dev/sdX
    
    The above formats the volume for 8 nodes with a 4K block size and a 4K cluster size.
  28. What does the number of node slots during format refer to?
    The number of node slots specifies the number of nodes that can concurrently mount the volume. This number is specified during format and can be increased using tunefs.ocfs2. This number cannot be decreased.
  29. What should I consider when determining the number of node slots?
    OCFS2 allocates system files, like Journal, for each node slot. So as to not to waste space, one should specify a number within the ballpark of the actual number of nodes. Also, as this number can be increased, there is no need to specify a much larger number than one plans for mounting the volume.
  30. Does the number of node slots have to be the same for all volumes?
    No. This number can be different for each volume.
  31. What block size should I use?
    A block size is the smallest unit of space addressable by the file system. OCFS2 supports block sizes of 512 bytes, 1K, 2K and 4K. The block size cannot be changed after the format. For most volume sizes, a 4K size is recommended. On the other hand, the 512 bytes block is never recommended.
  32. What cluster size should I use?
    A cluster size is the smallest unit of space allocated to a file to hold the data. OCFS2 supports cluster sizes of 4K, 8K, 16K, 32K, 64K, 128K, 256K, 512K and 1M. For Oracle home, use 4K cluster size. For database volumes, use any value equal to or larger than the database blocksize. This ensures that the entire Oracle data block will be contiguous on disk. Earlier, we used to recommend 128K cluster size for the database volumes. The only problem with that value was that it could lead to space wastage if the volume was used to store many small files. The new recommendation gives a hard lower limit and allows users to pick any larger value.
  33. Any advantage of labelling the volumes?
    As in a shared disk environment, the disk name (/dev/sdX) for a particular device be different on different nodes, labelling becomes a must for easy identification. You could also use labels to identify volumes during mount.
    	# mount -L "label" /dir
    
    The volume label is changeable using the tunefs.ocfs2 utility.

    RESIZE

  34. Can OCFS2 file systems be grown in size?
    Yes, you can grow an OCFS2 file system using tunefs.ocfs2. It should be noted that the tool will only resize the file system and not the underlying partition. You can use fdisk(8) (or any appropriate tool for your disk array) to resize the partition.
  35. What do I need to know to use fdisk(8) to resize the partition?
    To grow a partition using fdisk(8), you will have to delete it and recreate it with a larger size. When recreating it, ensure you specify the same starting disk cylinder as before and a ending disk cylinder that is greater than the existing one. Otherwise, not only will the resize operation fail, but you may lose your entire file system. Backup your data before performing this task.
  36. Short of reboot, how do I get the other nodes in the cluster to see the resized partition?
    Use blockdev(8) to rescan the partition table of the device on the other nodes in the cluster.
    	# blockdev --rereadpt /dev/sdX
    
  37. What is the tunefs.ocfs2 syntax for resizing the file system?
    To grow a file system to the end of the resized partition, do:
    	# tunefs.ocfs2 -S /dev/sdX
    
    For more, refer to the tunefs.ocfs2 manpage.
  38. Can the OCFS2 file system be grown while the file system is in use?
    No. tunefs.ocfs2 1.2.2 only allows offline resize. i.e., the file system cannot be mounted on any node in the cluster. The online resize capability will be added later.
  39. Can the OCFS2 file system be shrunk in size?
    No. We have no current plans on providing this functionality. However, if you find this feature useful, file an enhancement request on bugzilla listing your reasons for the same.

    MOUNT

  40. How do I mount the volume?
    You could either use the console or use mount directly. For console, refer to the user's guide.
    	# mount -t ocfs2 /dev/sdX /dir
    
    The above command will mount device /dev/sdX on directory /dir.
  41. How do I mount by label?
    To mount by label do:
    	# mount -L "label" /dir
    
  42. What entry to I add to /etc/fstab to mount an ocfs2 volume?
    Add the following:
    	/dev/sdX	/dir	ocfs2	_netdev		0	0
    
    The _netdev option indicates that the devices needs to be mounted after the network is up.
  43. What do I need to do to mount OCFS2 volumes on boot?
  44. How do I know my volume is mounted?
  45. What are the /config and /dlm mountpoints for?
    OCFS2 comes bundled with two in-memory filesystems configfs and ocfs2_dlmfs. configfs is used by the ocfs2 tools to communicate to the in-kernel node manager the list of nodes in the cluster and to the in-kernel heartbeat thread the resource to heartbeat on. ocfs2_dlmfs is used by ocfs2 tools to communicate with the in-kernel dlm to take and release clusterwide locks on resources.
  46. Why does it take so much time to mount the volume?
    It takes around 5 secs for a volume to mount. It does so so as to let the heartbeat thread stabilize. In a later release, we plan to add support for a global heartbeat, which will make most mounts instant.
  47. Why does it take so much time to umount the volume?
    During umount, the dlm has to migrate all the mastered lockres' to an another node in the cluster. In 1.2, the lockres migration is a synchronous operation. We are looking into making it asynchronous so as to reduce the time it takes to migrate the lockres'. (While we have improved this performance in 1.2.5, the task of asynchronously migrating lockres' has been pushed to the 1.4 time frame.) To find the number of lockres in all dlm domains, do:
    	# cat /proc/fs/ocfs2_dlm/*/stat
    	local=60624, remote=1, unknown=0, key=0x8619a8da
    
    local refers to locally mastered lockres'.

    ORACLE RAC

  48. Any special flags to run Oracle RAC?
    OCFS2 volumes containing the Voting diskfile (CRS), Cluster registry (OCR), Data files, Redo logs, Archive logs and Control files must be mounted with the datavolume and nointr mount options. The datavolume option ensures that the Oracle processes opens these files with the o_direct flag. The nointr option ensures that the ios are not interrupted by signals.
    	# mount -o datavolume,nointr -t ocfs2 /dev/sda1 /u01/db
    
  49. What about the volume containing Oracle home?
    Oracle home volume should be mounted normally, that is, without the datavolume and nointr mount options. These mount options are only relevant for Oracle files listed above.
    	# mount -t ocfs2 /dev/sdb1 /software/orahome
    
    Also as OCFS2 does not currently support shared writeable mmap, the health check (GIMH) file $ORACLE_HOME/dbs/hc_ORACLESID.dat and the ASM file $ASM_HOME/dbs/ab_ORACLESID.dat should be symlinked to local filesystem. We expect to support shared writeable mmap in the OCFS2 1.4 release.
  50. Does that mean I cannot have my data file and Oracle home on the same volume?
    Yes. The volume containing the Oracle data files, redo-logs, etc. should never be on the same volume as the distribution (including the trace logs like, alert.log).
  51. Any other information I should be aware off?
    The 1.2.3 release of OCFS2 does not update the modification time on the inode across the cluster for non-extending writes. However, the time will be locally updated in the cached inodes. This leads to one observing different times (ls -l) for the same file on different nodes on the cluster.
    While this does not affect most uses of the filesystem, as one variably changes the file size during write, the one usage where this is most commonly experienced is with Oracle datafiles and redologs. This is because Oracle rarely resizes these files and thus almost all writes are non-extending.
    In OCFS2 1.4, we intend to fix this by updating modification times for all writes while providing an opt-out mount option (nocmtime) for users who would prefer to avoid the performance overhead associated with this feature.

    MIGRATE DATA FROM OCFS (RELEASE 1) TO OCFS2

  52. Can I mount OCFS volumes as OCFS2?
    No. OCFS and OCFS2 are not on-disk compatible. We had to break the compatibility in order to add many of the new features. At the same time, we have added enough flexibility in the new disk layout so as to maintain backward compatibility in the future.
  53. Can OCFS volumes and OCFS2 volumes be mounted on the same machine simultaneously?
    No. OCFS only works on 2.4 linux kernels (Red Hat's AS2.1/EL3 and SuSE's SLES8). OCFS2, on the other hand, only works on the 2.6 kernels (RHEL4, SLES9 and SLES10).
  54. Can I access my OCFS volume on 2.6 kernels (SLES9/SLES10/RHEL4)?
    Yes, you can access the OCFS volume on 2.6 kernels using FSCat tools, fsls and fscp. These tools can access the OCFS volumes at the device layer, to list and copy the files to another filesystem. FSCat tools are available on oss.oracle.com.
  55. Can I in-place convert my OCFS volume to OCFS2?
    No. The on-disk layout of OCFS and OCFS2 are sufficiently different that it would require a third disk (as a temporary buffer) inorder to in-place upgrade the volume. With that in mind, it was decided not to develop such a tool but instead provide tools to copy data from OCFS without one having to mount it.
  56. What is the quickest way to move data from OCFS to OCFS2?
    Quickest would mean having to perform the minimal number of copies. If you have the current backup on a non-OCFS volume accessible from the 2.6 kernel install, then all you would need to do is to retore the backup on the OCFS2 volume(s). If you do not have a backup but have a setup in which the system containing the OCFS2 volumes can access the disks containing the OCFS volume, you can use the FSCat tools to extract data from the OCFS volume and copy onto OCFS2.

    COREUTILS

  57. Like with OCFS (Release 1), do I need to use o_direct enabled tools to perform cp, mv, tar, etc.?
    No. OCFS2 does not need the o_direct enabled tools. The file system allows processes to open files in both o_direct and bufferred mode concurrently.

    EXPORTING VIA NFS

  58. Can I export an OCFS2 file system via NFS?
    Yes, you can export files on OCFS2 via the standard Linux NFS server. Please note that only NFS version 3 and above will work. In practice, this means clients need to be running a 2.4.x kernel or above.
  59. Is there no solution for the NFS v2 clients?
    NFS v2 clients can work if the server exports the volumes with the no_subtree_check option. However, this has some security implications that is documented in the exports manpage.

    TROUBLESHOOTING

  60. How do I enable and disable filesystem tracing?
    To list all the debug bits along with their statuses, do:
    	# debugfs.ocfs2 -l
    
    To enable tracing the bit SUPER, do:
    	# debugfs.ocfs2 -l SUPER allow
    
    To disable tracing the bit SUPER, do:
    	# debugfs.ocfs2 -l SUPER off
    
    To totally turn off tracing the SUPER bit, as in, turn off tracing even if some other bit is enabled for the same, do:
    	# debugfs.ocfs2 -l SUPER deny
    
    To enable heartbeat tracing, do:
    	# debugfs.ocfs2 -l HEARTBEAT ENTRY EXIT allow
    
    To disable heartbeat tracing, do:
    	# debugfs.ocfs2 -l HEARTBEAT off ENTRY EXIT deny
    
  61. How do I get a list of filesystem locks and their statuses?
    OCFS2 1.0.9+ has this feature. To get this list, do:
  62. How do I read the fs_locks output?
    Let's look at a sample output:
    	Lockres: M000000000000000006672078b84822  Mode: Protected Read
    	Flags: Initialized Attached
    	RO Holders: 0  EX Holders: 0
    	Pending Action: None  Pending Unlock Action: None
    	Requested Mode: Protected Read  Blocking Mode: Invalid
    
    First thing to note is the Lockres, which is the lockname. The dlm identifies resources using locknames. A lockname is a combination of a lock type (S superblock, M metadata, D filedata, R rename, W readwrite), inode number and generation.
    To get the inode number and generation from lockname, do:
    	#echo "stat " | debugfs.ocfs2 -n /dev/sdX
    	Inode: 419616   Mode: 0666   Generation: 2025343010 (0x78b84822)
    	....
    
    To map the lockname to a directory entry, do:
    	# echo "locate " | debugfs.ocfs2 -n /dev/sdX
    	419616  /linux-2.6.15/arch/i386/kernel/semaphore.c
    
    One could also provide the inode number instead of the lockname.
    	# echo "locate <419616>" | debugfs.ocfs2 -n /dev/sdX
    	419616  /linux-2.6.15/arch/i386/kernel/semaphore.c
    
    To get a lockname from a directory entry, do:
    	# echo "encode /linux-2.6.15/arch/i386/kernel/semaphore.c" | debugfs.ocfs2 -n /dev/sdX
    	M000000000000000006672078b84822 D000000000000000006672078b84822 W000000000000000006672078b84822
    
    The first is the Metadata lock, then Data lock and last ReadWrite lock for the same resource.

    The DLM supports 3 lock modes: NL no lock, PR protected read and EX exclusive.

    If you have a dlm hang, the resource to look for would be one with the "Busy" flag set.

    The next step would be to query the dlm for the lock resource.

    Note: The dlm debugging is still a work in progress.

    To do dlm debugging, first one needs to know the dlm domain, which matches the volume UUID.
    	# echo "stats" | debugfs.ocfs2 -n /dev/sdX | grep UUID: | while read a b ; do echo $b ; done
    	82DA8137A49A47E4B187F74E09FBBB4B
    
    Then do:
    	# echo R dlm_domain lockname > /proc/fs/ocfs2_dlm/debug
    
    For example:
    	# echo R 82DA8137A49A47E4B187F74E09FBBB4B M000000000000000006672078b84822 > /proc/fs/ocfs2_dlm/debug
    	# dmesg | tail
    	struct dlm_ctxt: 82DA8137A49A47E4B187F74E09FBBB4B, node=79, key=965960985
    	lockres: M000000000000000006672078b84822, owner=75, state=0 last used: 0, on purge list: no
    	  granted queue:
    	    type=3, conv=-1, node=79, cookie=11673330234144325711, ast=(empty=y,pend=n), bast=(empty=y,pend=n)
    	  converting queue:
    	  blocked queue:
    
    It shows that the lock is mastered by node 75 and that node 79 has been granted a PR lock on the resource.

    This is just to give a flavor of dlm debugging.

    LIMITS

  63. Is there a limit to the number of subdirectories in a directory?
    Yes. OCFS2 currently allows up to 32000 subdirectories. While this limit could be increased, we will not be doing it till we implement some kind of efficient name lookup (htree, etc.).
  64. Is there a limit to the size of an ocfs2 file system?
    Yes, current software addresses block numbers with 32 bits. So the file system device is limited to (2 ^ 32) * blocksize (see mkfs -b). With a 4KB block size this amounts to a 16TB file system. This block addressing limit will be relaxed in future software. At that point the limit becomes addressing clusters of 1MB each with 32 bits which leads to a 4PB file system.

    SYSTEM FILES

  65. What are system files?
    System files are used to store standard filesystem metadata like bitmaps, journals, etc. Storing this information in files in a directory allows OCFS2 to be extensible. These system files can be accessed using debugfs.ocfs2. To list the system files, do:
    	# echo "ls -l //" | debugfs.ocfs2 -n /dev/sdX
            	18        16       1      2  .
            	18        16       2      2  ..
            	19        24       10     1  bad_blocks
            	20        32       18     1  global_inode_alloc
            	21        20       8      1  slot_map
            	22        24       9      1  heartbeat
            	23        28       13     1  global_bitmap
            	24        28       15     2  orphan_dir:0000
            	25        32       17     1  extent_alloc:0000
            	26        28       16     1  inode_alloc:0000
            	27        24       12     1  journal:0000
            	28        28       16     1  local_alloc:0000
            	29        3796     17     1  truncate_log:0000
    
    The first column lists the block number.
  66. Why do some files have numbers at the end?
    There are two types of files, global and local. Global files are for all the nodes, while local, like journal:0000, are node specific. The set of local files used by a node is determined by the slot mapping of that node. The numbers at the end of the system file name is the slot#. To list the slot maps, do:
    	# echo "slotmap" | debugfs.ocfs2 -n /dev/sdX
           	Slot#   Node#
                0      39
           	    1      40
                2      41
           	    3      42
    

    HEARTBEAT

  67. How does the disk heartbeat work?
    Every node writes every two secs to its block in the heartbeat system file. The block offset is equal to its global node number. So node 0 writes to the first block, node 1 to the second, etc. All the nodes also read the heartbeat sysfile every two secs. As long as the timestamp is changing, that node is deemed alive.
  68. When is a node deemed dead?
    An active node is deemed dead if it does not update its timestamp for O2CB_HEARTBEAT_THRESHOLD (default=31) loops. Once a node is deemed dead, the surviving node which manages to cluster lock the dead node's journal, recovers it by replaying the journal.
  69. What about self fencing?
    A node self-fences if it fails to update its timestamp for ((O2CB_HEARTBEAT_THRESHOLD - 1) * 2) secs. The [o2hb-xx] kernel thread, after every timestamp write, sets a timer to panic the system after that duration. If the next timestamp is written within that duration, as it should, it first cancels that timer before setting up a new one. This way it ensures the system will self fence if for some reason the [o2hb-x] kernel thread is unable to update the timestamp and thus be deemed dead by other nodes in the cluster.
  70. How can one change the parameter value of O2CB_HEARTBEAT_THRESHOLD?
    This parameter value could be changed by adding it to /etc/sysconfig/o2cb and RESTARTING the O2CB cluster. This value should be the SAME on ALL the nodes in the cluster.
  71. What should one set O2CB_HEARTBEAT_THRESHOLD to?
    It should be set to the timeout value of the io layer. Most multipath solutions have a timeout ranging from 60 secs to 120 secs. For 60 secs, set it to 31. For 120 secs, set it to 61.
    	O2CB_HEARTBEAT_THRESHOLD = (((timeout in secs) / 2) + 1)
    
  72. How does one check the current active O2CB_HEARTBEAT_THRESHOLD value?
    	# cat /proc/fs/ocfs2_nodemanager/hb_dead_threshold
    	7
    
  73. What if a node umounts a volume?
    During umount, the node will broadcast to all the nodes that have mounted that volume to drop that node from its node maps. As the journal is shutdown before this broadcast, any node crash after this point is ignored as there is no need for recovery.
  74. I encounter "Kernel panic - not syncing: ocfs2 is very sorry to be fencing this system by panicing" whenever I run a heavy io load?
    We have encountered a bug with the default CFQ io scheduler which causes a process doing heavy io to temporarily starve out other processes. While this is not fatal for most environments, it is for OCFS2 as we expect the hb thread to reading from and writing to the hb area atleast once every 12 secs (default). This bug has been addressed by Red Hat in RHEL4 U4 (2.6.9-42.EL) and Novell in SLES9 SP3 (2.6.5-7.257). If you wish to use the DEADLINE io scheduler, you could do so by appending "elevator=deadline" to the kernel command line as follows:

    To see the current kernel command line, do:
    	# cat /proc/cmdline
    

    QUORUM AND FENCING

  75. What is a quorum?
    A quorum is a designation given to a group of nodes in a cluster which are still allowed to operate on shared storage. It comes up when there is a failure in the cluster which breaks the nodes up into groups which can communicate in their groups and with the shared storage but not between groups.
  76. How does OCFS2's cluster services define a quorum? The quorum decision is made by a single node based on the number of other nodes that are considered alive by heartbeating and the number of other nodes that are reachable via the network.
    A node has quorum when:
  77. What is fencing?
    Fencing is the act of forecefully removing a node from a cluster. A node with OCFS2 mounted will fence itself when it realizes that it doesn't have quorum in a degraded cluster. It does this so that other nodes won't get stuck trying to access its resources. Currently OCFS2 will panic the machine when it realizes it has to fence itself off from the cluster. As described above, it will do this when it sees more nodes heartbeating than it has connectivity to and fails the quorum test.
    Due to user reports of nodes hanging during fencing, OCFS2 1.2.5 no longer uses "panic" for fencing. Instead, by default, it uses "machine restart". This should not only prevent nodes from hanging during fencing but also allow for nodes to quickly restart and rejoin the cluster. While this change is internal in nature, we are documenting this so as to make users aware that they are no longer going to see the familiar panic stack trace during fencing. Instead they will see the message "*** ocfs2 is very sorry to be fencing this system by restarting ***" and that too probably only as part of the messages captured on the netdump/netconsole server.
    If perchance the user wishes to use panic to fence (maybe to see the familiar oops stack trace or on the advise of customer support to diagnose frequent reboots), one can do so by issuing the following command after the O2CB cluster is online.
    	# echo 1 > /proc/fs/ocfs2_nodemanager/fence_method
    
    Please note that this change is local to a node.
  78. How does a node decide that it has connectivity with another?
    When a node sees another come to life via heartbeating it will try and establish a TCP connection to that newly live node. It considers that other node connected as long as the TCP connection persists and the connection is not idle for O2CB_IDLE_TIMEOUT_MS. Once that TCP connection is closed or idle it will not be reestablished until heartbeat thinks the other node has died and come back alive.
  79. How long does the quorum process take?
    First a node will realize that it doesn't have connectivity with another node. This can happen immediately if the connection is closed but can take a maximum of O2CB_IDLE_TIMEOUT_MS idle time. Then the node must wait long enough to give heartbeating a chance to declare the node dead. It does this by waiting two iterations longer than the number of iterations needed to consider a node dead (see the Heartbeat section of this FAQ). The current default of 31 iterations of 2 seconds results in waiting for 33 iterations or 66 seconds. By default, then, a maximum of 96 seconds can pass from the time a network fault occurs until a node fences itself.
  80. How can one avoid a node from panic-ing when one shutdowns the other node in a 2-node cluster?
    This typically means that the network is shutting down before all the OCFS2 volumes are being umounted. Ensure the ocfs2 init script is enabled. This script ensures that the OCFS2 volumes are umounted before the network is shutdown. To check whether the service is enabled, do:
           	# chkconfig --list ocfs2
           	ocfs2     0:off   1:off   2:on    3:on    4:on    5:on    6:off
    
  81. How does one list out the startup and shutdown ordering of the OCFS2 related services?
    Please note that the default ordering in the ocfs2 scripts only include the network service and not any shared-device specific service, like iscsi. If one is using iscsi or any shared device requiring a service to be started and shutdown, please ensure that that service runs before and shutsdown after the ocfs2 init service.

    NOVELL'S SLES9 and SLES10

  82. Why are OCFS2 packages for SLES9 and SLES10 not made available on oss.oracle.com?
    OCFS2 packages for SLES9 and SELS10 are available directly from Novell as part of the kernel. Same is true for the various Asianux distributions and for ubuntu. As OCFS2 is now part of the mainline kernel, we expect more distributions to bundle the product with the kernel.
  83. What versions of OCFS2 are available with SLES9 and how do they match with the Red Hat versions available on oss.oracle.com?
    As both Novell and Oracle ship OCFS2 on different schedules, the package versions do not match. We expect to resolve itself over time as the number of patch fixes reduce. Novell is shipping two SLES9 releases, viz., SP2 and SP3.
  84. What versions of OCFS2 are available with SLES10? SLES10 is currently shipping OCFS2 1.2.3. SLES10 SP1 is currently shipping 1.2.5-1.

    RELEASE 1.2

  85. What is new in OCFS2 1.2?
    OCFS2 1.2 has two new features:
  86. Do I need to re-make the volume when upgrading?
    No. OCFS2 1.2 is fully on-disk compatible with 1.0.
  87. Do I need to upgrade anything else?
    Yes, the tools needs to be upgraded to ocfs2-tools 1.2. ocfs2-tools 1.0 will not work with OCFS2 1.2 nor will 1.2 tools work with 1.0 modules.

    UPGRADE TO THE LATEST RELEASE

  88. How do I upgrade to the latest release?
  89. Can I do a rolling upgrade from 1.2.3 to 1.2.4?
    No. The network protocol had to be updated in 1.2.4 to allow for proper reference counting of lockres' across the cluster. This fix was necessary to fix races encountered during lockres purge and migrate. Effectively, one cannot run 1.2.4 on one node while another node is still on an earlier release (1.2.3 or older).
  90. Can I do a rolling upgrade from 1.2.4 to 1.2.5?
    No. The network protocol had to be updated in 1.2.5 to ensure all nodes were using the same O2CB timeouts. Effectively, one cannot run 1.2.5 on one node while another node is still on an earlier release. (For the record, the protocol remained the same between 1.2.0 to 1.2.3 before changing in 1.2.4 and 1.2.5.)
  91. Can I do a rolling upgrade from 1.2.6 to 1.2.7 on EL5?
    Yes. The network protocol is fully compatible across both releases.
  92. Can I do a rolling upgrade from 1.2.5 to 1.2.7 on EL4?
    Yes. However, there is a catch. While the network protocol is fully compatible across the two releases, the default cluster timeouts are not. So if you were using the default timeouts, you will have to specifically set those timeouts on the new nodes using service o2cb configure command. Use service o2cb status to review current timeouts.
    Users that are not careful with the above are likely to encounter failed mounts on the upgraded node. dmesg will indicate the differing timeout values.
  93. Can I do a rolling upgrade from 1.2.7 to 1.2.8 or 1.2.9 on EL4 and EL5?
    Yes. OCFS2 1.2.7, 1.2.8 and 1.2.9 are fully compatible. Users upgrading to 1.2.8/9 from 1.2.5/1.2.6 can expect the same behaviour as described above for upgrading to 1.2.7.
  94. After upgrade I am getting the following error on mount "mount.ocfs2: Invalid argument while mounting /dev/sda6 on /ocfs".
    Do "dmesg | tail". If you see the error:
    ocfs2_parse_options:523 ERROR: Unrecognized mount option "heartbeat=local" or missing value
    
    it means that you are trying to use the 1.2 tools and 1.0 modules. Ensure that you have unloaded the 1.0 modules and installed and loaded the 1.2 modules. Use modinfo to determine the version of the module installed and/or loaded.
  95. The cluster fails to load. What do I do?
    Check "demsg | tail" for any relevant errors. One common error is as follows:
    SELinux: initialized (dev configfs, type configfs), not configured for labeling audit(1139964740.184:2): avc:  denied  { mount } for  ...
    
    The above error indicates that you have SELinux activated. A bug in SELinux does not allow configfs to mount. Disable SELinux by setting "SELINUX=disabled" in /etc/selinux/config. Change is activated on reboot.

    PROCESSES

  96. List and describe all OCFS2 threads?
    [o2net]
    One per node. Is a workqueue thread started when the cluster is brought online and stopped when offline. It handles the network communication for all threads. It gets the list of active nodes from the o2hb thread and sets up tcp/ip communication channels with each active node. It sends regular keepalive packets to detect any interruption on the channels.
    [user_dlm]
    One per node. Is a workqueue thread started when dlmfs is loaded and stopped on unload. (dlmfs is an in-memory file system which allows user space processes to access the dlm in kernel to lock and unlock resources.) Handles lock downconverts when requested by other nodes.
    [ocfs2_wq]
    One per node. Is a workqueue thread started when ocfs2 module is loaded and stopped on unload. Handles blockable file system tasks like truncate log flush, orphan dir recovery and local alloc recovery, which involve taking dlm locks. Various code paths queue tasks to this thread. For example, ocfs2rec queues orphan dir recovery so that while the task is kicked off as part of recovery, its completion does not affect the recovery time.
    [o2hb-14C29A7392]
    One per heartbeat device. Is a kernel thread started when the heartbeat region is populated in configfs and stopped when it is removed. It writes every 2 secs to its block in the heartbeat region to indicate to other nodes that that node is alive. It also reads the region to maintain a nodemap of live nodes. It notifies o2net and dlm any changes in the nodemap.
    [ocfs2vote-0]
    One per mount. Is a kernel thread started when a volume is mounted and stopped on umount. It downgrades locks when requested by other nodes in reponse to blocking ASTs (BASTs). It also fixes up the dentry cache in reponse to files unlinked or renamed on other nodes.
    [dlm_thread]
    One per dlm domain. Is a kernel thread started when a dlm domain is created and stopped when destroyed. This is the core dlm which maintains the list of lock resources and handles the cluster locking infrastructure.
    [dlm_reco_thread]
    One per dlm domain. Is a kernel thread which handles dlm recovery whenever a node dies. If the node is the dlm recovery master, it remasters all the locks owned by the dead node.
    [dlm_wq]
    One per dlm domain. Is a workqueue thread. o2net queues dlm tasks on this thread.
    [kjournald]
    One per mount. Is used as OCFS2 uses JDB for journalling.
    [ocfs2cmt-0]
    One per mount. Is a kernel thread started when a volume is mounted and stopped on umount. Works in conjunction with kjournald.
    [ocfs2rec-0]
    Is started whenever another node needs to be be recovered. This could be either on mount when it discovers a dirty journal or during operation when hb detects a dead node. ocfs2rec handles the file system recovery and it runs after the dlm has finished its recovery.

    BUILD RPMS FOR HOTFIX KERNELS

  97. How to build OCFS2 packages for a hotfix kernel?
    The packages will be in %_rpmdir.
  98. Are the self-built packages officially supported by Oracle Support?
    No. Oracle Support does not provide support for self-built modules. If you wish official support, contact Oracle via Support or the ocfs2-users mailing list with the link to the hotfix kernel (kernel-devel and kernel-src rpms).

    BACKUP SUPER BLOCK

  99. What is a Backup Super block? A backup super block is a copy of the super block. As the super block is typically located close to the start of the device, it is susceptible to be overwritten, say, by an errant write (dd if=file of=/dev/sdX). Moreover, as the super block stores critical information that is hard to recreate, it becomes important to backup the block and use it when the super block gets corrupted.
  100. Where are the backup super blocks located? In OCFS2, the super blocks are backed up to blocks at the 1G, 4G, 16G, 64G, 256G and 1T byte offsets. The actual number of backups depend on the size of the device. It should be noted that the super block is not backed up on devices smaller than 1G.
  101. How does one enable this feature? mkfs.ocfs2 1.2.3 or later automatically backs up super blocks on devices larger than 1G. One can disable this by using the --no-backup-super option.
  102. How do I detect whether the super blocks are backed up on a device?
    	# debugfs.ocfs2 -R "stats" /dev/sdX | grep "Feature Compat"
            	Feature Compat: 1 BackupSuper
    
  103. How do I backup the super block on a device formatted by an older mkfs.ocfs2? tunefs.ocfs2 1.2.3 or later can attempt to retroactively backup the super block.
    	# tunefs.ocfs2 --backup-super /dev/sdX
    	tunefs.ocfs2 1.2.3
    	Adding backup superblock for the volume
    	Proceed (y/N): y
    	Backed up Superblock.
    	Wrote Superblock
    
    However, it is quite possible that one or more backup locations are in use by the file system. (tunefs.ocfs2 backs up the block only if all the backup locations are unused.)
    	# tunefs.ocfs2 --backup-super /dev/sdX
    	tunefs.ocfs2 1.2.3
    	tunefs.ocfs2: block 262144 is in use.
    	tunefs.ocfs2: block 4194304 is in use.
    	tunefs.ocfs2: Cannot enable backup superblock as backup blocks are in use
    
    If so, use the verify_backup_super script to list out the objects using these blocks.
    	# ./verify_backup_super /dev/sdX
    	Locating inodes using blocks 262144 1048576 4194304 on device /dev/sdX
            	Block#            Inode             Block Offset   
            	262144            27                65058          
            	1048576           Unused                           
            	4194304           4161791           25             
    	Matching inodes to object names
            	27      //journal:0003
            	4161791 /src/kernel/linux-2.6.19/drivers/scsi/BusLogic.c
    
    If the object happens to be user created, move that object temporarily to an another volume before re-attempting the operation. However, this will not work if one or more blocks are being used by a system file (shown starting with double slashes //), say, a journal.
  104. How do I ask fsck.ocfs2 to use a backup super block? To recover a volume using the second backup super block, do:
    	# fsck.ocfs2 -f -r 2 /dev/sdX
    	[RECOVER_BACKUP_SUPERBLOCK] Recover superblock information from backup block#1048576?  n
    	Checking OCFS2 filesystem in /dev/sdX
      	label:              myvolume
      	uuid:               4d 1d 1f f3 24 01 4d 3f 82 4c e2 67 0c b2 94 f3 
      	number of blocks:   13107196
      	bytes per block:    4096
      	number of clusters: 13107196
      	bytes per cluster:  4096
      	max slots:          4
    
    	/dev/sdX was run with -f, check forced.
    	Pass 0a: Checking cluster allocation chains
    	Pass 0b: Checking inode allocation chains
    	Pass 0c: Checking extent block allocation chains
    	Pass 1: Checking inodes and blocks.
    	Pass 2: Checking directory entries.
    	Pass 3: Checking directory connectivity.
    	Pass 4a: checking for orphaned inodes
    	Pass 4b: Checking inodes link counts.
    	All passes succeeded.
    
    For more, refer to the man pages.

    CONFIGURING CLUSTER TIMEOUTS

  105. List and describe all the configurable timeouts in the O2CB cluster stack? OCFS2 1.2.5 has 4 different configurable O2CB cluster timeouts:
  106. What are the recommended timeout values? As timeout values depend on the hardware being used, there is no one set of recommended values. For e.g., users of multipath io should set the disk heartbeat threshold to atleast 60 secs, if not 120 secs. Similarly, users of Network bonding should set the network idle timeout to atleast 30 secs, if not 60 secs.
  107. What are the currect defaults for the cluster timeouts? The timeouts were updated in the 1.2.6 release to the following:
    	O2CB_HEARTBEAT_THRESHOLD = 31
    	O2CB_IDLE_TIMEOUT_MS = 30000
    	O2CB_KEEPALIVE_DELAY_MS = 2000
    	O2CB_RECONNECT_DELAY_MS = 2000
    

  108. Can one change these timeout values in a round robin fashion? No. The o2net handshake protocol ensures that all the timeout values for both the nodes are consistent and fails if any value differs. This failed connection results in a failed mount, the reason for which is always listed in dmesg.
  109. How does one set these O2CB timeouts? Umount all OCFS2 volumes and shutdown the O2CB cluster. If not already, upgrade to OCFS2 1.2.5+ and Tools 1.2.4+. Then use o2cb configure to set the new values. Do the same on all nodes. Start mounting volumes only after the timeouts have been set on all nodes.
    	# service o2cb configure
    	Configuring the O2CB driver.
    
    	This will configure the on-boot properties of the O2CB driver.
    	The following questions will determine whether the driver is loaded on
    	boot.  The current values will be shown in brackets ('[]').  Hitting
    	 without typing an answer will keep that current value.  Ctrl-C
    	will abort.
    
    	Load O2CB driver on boot (y/n) [n]: y
    	Cluster to start on boot (Enter "none" to clear) []: mycluster
    	Specify heartbeat dead threshold (>=7) [7]: 31
    	Specify network idle timeout in ms (>=5000) [10000]: 30000
    	Specify network keepalive delay in ms (>=1000) [5000]: 2000
    	Specify network reconnect delay in ms (>=2000) [2000]: 2000
    	Writing O2CB configuration: OK
    	Starting O2CB cluster mycluster: OK
    
  110. How to find the O2CB timeout values in effect?
    	# /etc/init.d/o2cb status
    	Module "configfs": Loaded
    	Filesystem "configfs": Mounted
    	Module "ocfs2_nodemanager": Loaded
    	Module "ocfs2_dlm": Loaded
    	Module "ocfs2_dlmfs": Loaded
    	Filesystem "ocfs2_dlmfs": Mounted
    	Checking O2CB cluster mycluster: Online
    	  Heartbeat dead threshold: 31
    	  Network idle timeout: 30000
    	  Network keepalive delay: 2000
    	  Network reconnect delay: 2000
    	Checking O2CB heartbeat: Not active
    
  111. Where are the O2CB timeout values stored?
    	# cat /etc/sysconfig/o2cb 
    	#
    	# This is a configuration file for automatic startup of the O2CB
    	# driver.  It is generated by running /etc/init.d/o2cb configure.
    	# Please use that method to modify this file
    	#
    
    	# O2CB_ENABELED: 'true' means to load the driver on boot.
    	O2CB_ENABLED=true
    
    	# O2CB_BOOTCLUSTER: If not empty, the name of a cluster to start.
    	O2CB_BOOTCLUSTER=mycluster
    
    	# O2CB_HEARTBEAT_THRESHOLD: Iterations before a node is considered dead.
    	O2CB_HEARTBEAT_THRESHOLD=31
    
    	# O2CB_IDLE_TIMEOUT_MS: Time in ms before a network connection is considered dead.
    	O2CB_IDLE_TIMEOUT_MS=30000
    
    	# O2CB_KEEPALIVE_DELAY_MS: Max time in ms before a keepalive packet is sent
    	O2CB_KEEPALIVE_DELAY_MS=2000
    
    	# O2CB_RECONNECT_DELAY_MS: Min time in ms between connection attempts
    	O2CB_RECONNECT_DELAY_MS=2000
    
    

    ENTERPRISE LINUX 5

  112. What are the changes in EL5 as compared to EL4 as it pertains to OCFS2? The in-memory filesystems, configfs and debugfs, have different mountpoints. configfs is mounted at /sys/kernel/config, instead of /config, while debugfs at /sys/kernel/debug, instead of /debug. (dlmfs still mounts at the old mountpoint /dlm.)