Re: [Moosefs-users] snapshots

[wkmail <wk...@bn...>]

Our experience has been uneven.  We do use it, because its convenient 
and we regard these as 'emergency' copies only and use more traditional 
backups for archival work.

However, on Large VM's (> 10G) we saw a lot of stress put on the system, 
based on the scrolling timeouts that start occuring right after you do 
the snapshot and continue until the entire copy has been made. Its even 
worse if you have lots deletions and replications going on at the same 
time and/or if the VM was busy.

On our test system, we could actually force VMs into read-only if we 
tried to stack up the Snapshots, which is easy to fall into on a shell 
script because the snapshot process exits and the snapshot files are 
created right away (the actual copy occurs when things start to change).

We ended up adding a line to sleep 1 minute for each GB of VM size 
before moving on to the next snapshot. Once we made that adjustment, the 
system works, though a certain sluggishness is noted.

It would be nice, if the actually snapshot data copy that occurs was 
optionally niced/delayed and made less intrusive like we can do with 
replication and deletions.

Of course with a VM, you also have the consistancy issue, but I assume 
you sync'ed/froze/shutdown  and/or were ok dealing with the 
fsck/myisamchk of your snapshot copy if you have to take it live <grin>.

-bill

On 12/13/2011 1:02 PM, Elliot Finley wrote:
> Hello all,
>
> Has anyone used snapshots extensively?  I'm just curios how robust
> they are.  I have 50+ VMs running with their virtual disk on MFS.  For
> backing up the VM images, I'd like to take a snapshot, copy it to
> remote location and then delete snapshot.
>
> Has anyone tried this or similar?  If so, would you mind sharing your
> experience?
>
> Thanks,
> Elliot
>
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