[Ocfs2-users] Debugging help / Guidance on architecture

[Sunil Mushran]

Damon Miller wrote:
> We're running a 3-node OCFS2 1.2.9 cluster with a 5-TB iSCSI block device as the backing store.  All machines are running CentOS, with the iSCSI target running CentOS 5.2 and the initiators running CentOS 4.7.  The purpose of the cluster is to evaluate alternatives to our current solution for replicating audio files which are generated from multiple PBX servers running Asterisk.
>
> We currently use Unison for file-level replication to and from a dedicated machine such that there are multiple copies of the audio tree--one per PBX server.  This allows us to quickly and easily move customers among our servers for load-balancing and disaster recovery purposes.  Unfortunately, we're encountering scalability problems with the Unison-based approach, e.g. conflicts, slow propogation time, etc.
>
> The hope was that moving to a clustered filesystem would improve propogation time, reduce conflicts, and allow us to scale more effectively.  I chose OCFS2 because it seemed the simplest solution architecturally and because of its certification by Oracle for use with the database product.  (My thought was that Oracle's certification requirements would likely supercede those of a general-purpose filesystem, though please correct me if this was naïve or misguided.)
>   

Oracle cert requirements are based on the Oracle db workload. General 
purpose
is all encompassing. There is no one certification that can be used for 
general
purpose as it is hard to capture the essence of all possible workloads. 
Having
said that, we have many users who are using it many different 
environments for
many years now. So you are not breaking any new ground.

> Having said all that, this morning around 7:00am EDT we began seeing OCFS2-related errors in one of our server's syslog.  Specifically:
>
> --
>
> May 15 07:08:00 cam-c6 kernel: o2net: no longer connected to node cam-p1 (num 1) at 10.10.89.110:7777
> May 15 07:08:00 cam-c6 kernel: (17170,0):ocfs2_broadcast_vote:731 ERROR: status = -112
> May 15 07:08:00 cam-c6 kernel: (17170,0):ocfs2_do_request_vote:804 ERROR: status = -112
> May 15 07:08:00 cam-c6 kernel: (17170,0):ocfs2_rename:1207 ERROR: status = -112
> May 15 07:08:00 cam-c6 kernel: (17170,0):ocfs2_broadcast_vote:731 ERROR: status = -107
> May 15 07:08:00 cam-c6 kernel: (17170,0):ocfs2_do_request_vote:804 ERROR: status = -107
> May 15 07:08:00 cam-c6 kernel: (17170,0):ocfs2_rename:1103 ERROR: status = -107
>
> [last message repeated many times]
>
> May 15 07:08:30 cam-c6 kernel: (4335,0):o2net_connect_expired:1585 ERROR: no connection established with n
> ode 1 after 30.0 seconds, giving up and returning errors.
>
> ...
>
> May 15 09:22:29 cam-c6 kernel: (4335,0):o2net_connect_expired:1585 ERROR: no connection established with n
> ode 1 after 30.0 seconds, giving up and returning errors.
>
> --
>
>
> This continued until 9:22am EDT, at which point one of our engineers manually rebooted the machine in an attempt to remedy the voicemail problems in response to Asterisk complaining of read/write problems to its voicemail tree.
>
> I was surprised OCFS2 didn't panic the kernel and automatically reboot the machine after the 30-second timeout.  I thought this was the default behavior and in fact I forced this condition by manually stopping the iSCSI daemon during preliminary testing.  Instead, the kernel complained for over two hours before someone manually rebooted the machine, at which point the cluster reconnected and resumed operation.  Is this expected?
>   

Connection between two nodes can snap. But it not reconnecting is strange.
One would think that 30 secs would be more than adequate for two nodes to
make a tcp connect. Do you have any firewalls in-between that could be
interfering?

> According to the relevant switch (a managed Cisco) there was no interruption in network connectivity between these two machines.  Neither server logged anything related to a network link failure so the only real information I have is from OCFS2.  Frankly I'm not sure how to proceed from here but I obviously want to address the reliability concerns this problem raises since we're considering OCFS2 for replacing our existing solution throughout our datacenters.
>   

If a firewall (iptables) is responsible, then it will not show up as
a link failure.

> I tried to map the numerical error codes -112 and -107 to specific problems based on the code ('tcp.c' and 'vote.c' in particular) but I was unsuccessful.
>   

ENOTCONN.

> In general, I suppose I'm curious if anyone has high-level feedback on the planned use of OCFS2 in this scenario.  Am I overcomplicating things?  Assuming the pilot works, we do plan to roll out a dedicated storage network which will include redundant switching, NICs, iSCSI targets with multiple paths to the physical storage, etc.  I just need to validate the basic approach at present.
>   

You email does not actually say how you are using the fs. You have mentioned
the older replication method. I would imagine that that is not your 
concern now.
The qs is: how are the nodes accessing the fs now? How many files do you 
have
in a dir? Are all nodes creating files in one dir? What other types of 
contention
is there?

OCFS2 can handle contention. The thing to remember is that contention even
on a single node will affect the performance. It only affects more in a 
clustered
setup.