[Lustre-discuss] Direct Snapshots of Lustre Filesystem & MDT size

[Nick Jennings]

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Thanks for the reply Brian, I actually did try several searches
regarding both questions, guess I just wasn't using the right keywords
(was getting much more unrelated info).

Couple comments below:


Brian J. Murrell wrote:
> On Fri, 2009-04-17 at 14:45 +0200, Nick Jennings | Technical Director
> wrote:
> 
>> Making a full copy of the
>> file system on another drive is already a backup in and of itself.
>> Doesn't this kind of defeat the purpose?
> 
> If the purpose is to make a backup, I don't see how that can be.

 Snapshotting combined with offsite backup is what I'm going for here.
Not a full copy of the filesystem on another set of (our) disks.


>> I can understand if you only
>> need a few files backed up, but if you have a 5TB file system, and want
>> a snapshot of it, it doesn't make much sense to make another 5TB LVM
>> slice, and copy everything there - then take a snapshot of that.
> 
> Yeah.  I don't recall reading anything like that in manual.  It does not
> sound terribly practical.  But then again, I suppose practicality is a
> function of the importance/value of your data.

 In the intro paragraph of section 15.3 (page 214 of the PDF) it says:
To get around this problem [performance loss of snapshotting main Lustre
filesystem], create a new, backup filesystem and periodically back up
new/changed files. Take periodic snapshots of this backup filesystem to
create a series of compact "full" backups.

 Maybe I'm misinterpreting that, but it seems to suggest coping any
important data to a separate partition (w/LVM+snapshotting). If all my
data is important, that's a full copy.



>>  The manual doesn't explain how to snapshot the lustre file system
>> directly. Is it not supported?
> 
> No.  The closest you can get is LVM snapshots of the targets and that
> comes with all the regular LVM snapshot caveats, again discussed on this
> list many times.

This is what I'm going for. By lustre filesystem I meant more
specifically, direct snapshotting of an OST, as opposed to a
copy/snapshot on another partition.

Is there a downside to having just one large OST per OSS, or is that
actually better? (assuming the storage target can only be connected to
one host at a time anyway)


- --
Nick Jennings
Technical Director
Creative Motion Design
www.creativemotiondesign.com
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