[Lustre-discuss] MDS

[Mag Gam]

Very nice insight.

Thanks Brian, Cliff, and Phil!



On Thu, Aug 7, 2008 at 11:14 AM, Brian J. Murrell <Brian.Murrell at sun.com> wrote:
> On Thu, 2008-08-07 at 10:51 -0700, Cliff White wrote:
>>
>> Just to be clear, there is a potential data loss issue due to the time
>> delta between the backup and the live system. Any transactions in play
>> that miss the snapshot could result in lost data, as the MDS will replay
>> transaction logs and delete orphans on startup. So testing on your live
>> system definately is for the brave.
>
> Indeed.  There are a couple of alternatives to consider.  I know your
> production MO will be to take an LVM snapshot of the running MDT and
> back that up, but if the MDT (i.e. filesystem) were shut down prior to
> the backup, what you restore should be an identical MDT which you could
> then start the filesystem against without the risks of in-play
> transactions and orphan deletion.  But indeed it is not a 100%
> reproduction of what would happen restoring from an in-production
> backup.
>
> Alternatively, rather than trying to start the OSTs against the restored
> MDT you could simply do a filesystem level (i.e. ldiskfs) comparison of
> the restored MDT against the production MDT.
>
> Indeed, there are other variations that you could use to satisfy
> yourself that the restore worked.
>
> I would highly suggest you do any of this testing either on a testbed
> (which you could build with a VirtualBox virtual cluster) or on your
> production system before you put production data on it.  It is good
> system deployment policy to have fully tested backup and restore
> policies before going live anyway.
>
> b.
>
>
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