[Ocfs2-users] Free space oddities on OCFS2

[Sunil Mushran]

1. The global bitmap in ocfs2 maps all the clusters on the disk. That 
includes,
the space used by the super block, root dir, system dir, system files, etc.
Hence the usage on a clean fs. Most of this space is being used by the 
journals.
# echo "stat //journal:0000" | debugfs.ocfs2 -n /dev/sdX

2. ocfs2 does not preallocate space for inodes. It allocates space on 
demand.
You can view the space allocated to inodes for slot 0 as follows:
# echo "stat //inode_alloc:0000" | debugfs.ocfs2 -n /dev/sdX

3. du does not reflect space used by filesystem metadata.

Robinson Maureira Castillo wrote:
> Hi all,
>
> I'm testing OCFS2 as a cluster filesystem for a mail system based on maildir, so basically the filesystem must be able to deal with lots of directories, and lots of small files.
>
> The first "oddity", is that when I mount a newly formated ocfs2 fs, it already contains used space:
>
> [root at ocfs1 /]# df /cgp02
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdb2             10710016    135004  10575012   2% /cgp02
>
> The info for that partition:
>
> [root at ocfs1 /]# fsck.ocfs2 -n /dev/sdb2
> Checking OCFS2 filesystem in /dev/sdb2:
>   label:              cgp02
>   uuid:               ad 2e 20 38 60 70 45 b8 97 68 48 d7 b9 88 5e 59
>   number of blocks:   10710016
>   bytes per block:    1024
>   number of clusters: 2677504
>   bytes per cluster:  4096
>   max slots:          2
>
> After creating 300 directories, and 300 files (2kB each) on each directory, renaming them, and then deleting, the df output is:
>
> [root at ocfs1 cgp02]# df /cgp02/
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdb2             10710016    228256  10481760   3% /cgp02
>
> I've created another partition, using these parameters:
>
> [root at ocfs1 cgp01]# fsck.ocfs2 -n /dev/sdb1
> Checking OCFS2 filesystem in /dev/sdb1:
>   label:              cgp01
>   uuid:               cf 1c 34 6b 10 87 45 37 84 fd 98 ea 8a 46 d2 7a
>   number of blocks:   2441724
>   bytes per block:    4096
>   number of clusters: 2441724
>   bytes per cluster:  4096
>   max slots:          2
>
> After creating 100000 accounts, and deleting them, the df output is:
>
> [root at ocfs1 cgp01]# df /cgp01
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdb1              9766896   2122080   7644816  22% /cgp01
>
> The usage reported by du in that directory:
>
> [root at ocfs1 cgp01]# du -sh .
> 23K     .
>
> If I create the 100000 accounts again...
>
> [root at ocfs1 example.lan]# df /cgp01/
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdb1              9766896   3342204   6424692  35% /cgp01
>
> [root at ocfs1 example.lan]# du -sh .
> 531M    .
>
> After a reboot...
>
> [root at ocfs1 ~]# df /cgp01/
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /dev/sdb1              9766896   3344956   6421940  35% /cgp01
>
> The application is using a 2-level hashing for directory creation, a typical user account resides on a hierarchy structure as shown below, and with those default files:
>
> [root at ocfs1 example.lan]# ll aa.sub/g.sub/test10110.macnt/
> total 1
> -rw-rw----  1 root mail 134 Aug  2 16:57 account.info
> -rw-rw----  1 root mail  78 Aug  2 16:57 account.settings
> -rw-rw----  1 root mail   0 Aug  2 16:57 INBOX.mbox
>
> Where are the other 2.8GB of data being used? Is this an expected behaviour? If so, then maybe I'm doing something terribly wrong, and I would appreciate an advise on what settings should I use for this scenario.
>
> On production systems, the size of the LUN presented is 1TB, 3 LUN per server, holding ~300000 user accounts, and expecting 1 million in a near future.
>
> Thanks in advance, and best regards,
> __________________________
> Robinson Maureira Castillo
> Soluciones Integrales S.A.
> Eleodoro Flores 2425, Ñuñoa, Santiago - Chile
> Central: (56 2) 411 9000   Fax: (56 2) 411 9001
> Directo: (56 2) 411 9047
> Móvil:   (56 9) 599 4987
> e-mail: rmaureira at solint.cl
>
> _______________________________________________
> Ocfs2-users mailing list
> Ocfs2-users at oss.oracle.com
> http://oss.oracle.com/mailman/listinfo/ocfs2-users
>