[CentOS] Dell Equallogic
Pasi Kärkkäinen
pasik at iki.fi
Wed Oct 14 18:04:20 UTC 2009
On Wed, Oct 14, 2009 at 10:36:01AM -0700, James A. Peltier wrote:
> On Tue, 13 Oct 2009, Pasi Kärkkäinen wrote:
>
> >
> >Hmm.. what kind of problems do you have with snapshots?
>
> Let's see
>
> They take up 16MB of space regardless of the amount of data that changes.
> A single bit changes and 16MB is taken up. This is not tunable.
>
EQL volumes are based on 'pages', that are (afaik) 16 MB in size.
So the minimum increment is 16 MB if you have changes on the volume.
This is expected.
> Mounting a snapshot requires the generation of a new UUID for the file
> system in order to be able to use it. Perhaps this is a XFS limitation,
> but unlike ZFS they aren't immediately available. We need to perform this
> action extensively to backup file systems and allow for quick data
> recovery.
>
This is not Equallogic problem, it's a limitation/feature of the
filesystem.
Taking snapshots in the Equallogic storage array takes only seconds, and
the snapshots are immediately available.
> There is no GNU/Linux interface to automating the snapshot process. Sure
> there is a telnet interface but it changes from version to version. I
> know because I've spoken with engineers to discuss this issue. I wrote
> software to talk to the EQL using the interface. There are talks of an
> SDK for developers but nothing has materialized.
>
I think Equallogic provides Perl samples how to take snapshots from
Linux/Unix scripts. I remember going through the scripts earlier.
So you can definitely integrate EQL stuff to your Linux environment.
> Don't get me wrong, it's a great device for cheap storage compared to
> competitors but there are obvious limitations that you need to address in
> your requirements if you intend to deploy it.
>
Well.. the stuff you mentioned isn't really Equallogic specific. It's
general stuff you need to sort out with any storage.
-- Pasi
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