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Antw: Re: Antw: Re: file system resource becomes inaccesible when any of the node goes down
>>> Muhammad Sharfuddin <M.Sharfuddin@nds.com.pk> schrieb am 07.07.2015 um 11:15 in
Nachricht <559B98A2.5060401@nds.com.pk>:

[...]
> I don't understand the advantage of Ocfs2 file system in such a setup.

The advantage depends on the alternatives: If two nodes both want to access the same filesystem, you can use OCFS2, NFS, or CIFS (list not complete). If only one node can access a filesystem, you could try any journaled filesystem (a fsck is needed after a node crash).

If you use NFS or CIFS, you shift the problem to another machine.

If you use a local filesystem, you need recovery, mount, and start of your application on a standby node.

With OCFS2 you'll have to wait for a few seconds before your application can continue.

Note that a usual SCSI disk with read-errors can also delay I/O significantly while retrying I/O.

Regards,
Ulrich


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Re: Antw: Re: Antw: Re: file system resource becomes inaccesible when any of the node goes down [ In reply to ]
On 2015-07-07T12:23:44, Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de> wrote:

> The advantage depends on the alternatives: If two nodes both want to access the same filesystem, you can use OCFS2, NFS, or CIFS (list not complete). If only one node can access a filesystem, you could try any journaled filesystem (a fsck is needed after a node crash).

A journaled file system does not require a fsck after a crash.

> If you use NFS or CIFS, you shift the problem to another machine.
>
> If you use a local filesystem, you need recovery, mount, and start of your application on a standby node.
>
> With OCFS2 you'll have to wait for a few seconds before your application can continue.

The recovery happens in the background with OCFS2 as well; the fs
replays the failed node's journal in the background. The actual time
saved by avoiding the "mount" is negligible.



Regards,
Lars

--
Architect Storage/HA
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Dilip Upmanyu, Graham Norton, HRB 21284 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde

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Re: Antw: Re: Antw: Re: file system resource becomes inaccesible when any of the node goes down [ In reply to ]
Hi Lars,

bist Du Dir hier sicher?

" After a crash the filesystem can very quickly be brought back on-line using the journal log reducing what could take
minutes using fsck to seconds with the added advantage that there is considerably less chance of data loss or
corruption."



Gruß
Ãœmit
>>> Lars Marowsky-Bree <lmb@suse.com> 7/9/2015 10:57 AM >>>
A journaled file system does not require a fsck after a crash.