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

Brian J. Murrell Brian.Murrell at Sun.COM
Fri Apr 17 05:57:58 PDT 2009


On Fri, 2009-04-17 at 14:45 +0200, Nick Jennings | Technical Director
wrote:
> 
> - - The first is recommended MDT size.

I think this is discussed, at least indirectly in the manual.  If not,
it most definitely has been discussed here several times.  The archives
will probably yield quite fruitful.

> How big should your MDT partition
> be? Does it depend on your estimated eventual size of your Lustre file
> system?

Yes.  In numbers of files, not total capacity.

> If so whats the ratio?

No ratio.  Number of files.

>  This kind of skirts the issue for me, ideally I'd like to backup the
> entire file system (everything is important).

Backup has been discussed on this many times as well.

> 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.

> 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.

>  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.

b.

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