[sheepdog-users] Sheepdog design architecture

[Andrew J. Hobbs]

This would be a good place for clarification on the recovery process 
when sheepdog is working in md mode.  Does the sheepdog client only 
attempt to recover the lost data to the remaining drives, or does it 
trigger a full blown recovery process?  Or is there a threshhold?  IE: 
if the available remaining capacity would hold the recovered data do 
that otherwise trigger a recovery/rebalance?

It's something of a maximization problem.  We want to minimize the 
amount of time running in a degraded state.  That includes failure 
states, recovery states, and rebuild states (on the RAID side) as all 
adversely affect performance.  What percentage of recoveries are 
triggered by disk failures as opposed to other issues (wiring guy 
unplugging a switch by accident, true story)?

Perhaps the best situation is a hybrid.  IE split the arrays into two 
RAID 5s of 8 disks each and running sheepdog md on top of them.  But 
without numbers, it's just a guess.

Gives me an idea though.  Think I'm going to instrument my cluster a bit 
to try an get some aggregate numbers during a recovery, both on node 
failure and disk failure on md nodes.

On 03/27/2014 03:10 AM, Valerio Pachera wrote:
> 2014-03-26 17:33 GMT+01:00 Giovanni Bellac <giovannib1979 at ymail.com>:
>> 2) Sheepdog Mutli Disk without using any RAID (just JOBD via RAID
>> Controller)
>> How reliable is the Sheepdog Multi Disk feature ?
>
> I would definitely avoid jbod.
> Each of your server is going to store 48T.
> If a single disk dies, all 48Tare going to be recovered in the cluster.
>
> I also suggest using sheepdog multi disk.
> In this case, if a disk dies, 3T are going to be recovered in the cluster.
>
> If you wish the controller takes care of a failed disk, I think raid 6
> may be the choise.
> You don't trigger any recover in case of a single disk failure but you
> have less storage for sheepdog it self.

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