[Dovecot] RAID1+md concat+XFS as mailstorage

Ed W lists at wildgooses.com
Thu Jun 28 19:20:26 EEST 2012

On 28/06/2012 14:06, Костырев Александр Алексеевич wrote:
>> - RAID1 pairs, plus some kind of intelligent overlay filesystem, eg
>> md-linear+XFS / BTRFS. With the filesystem aware of the underlying
>> arrangement it can theoretically optimise file placement and
>> dramatically increase write speeds for small files in the same manner
>> that RAID-0 theoretically achieves. (However, still no protection
>> against "silent" single drive corruption unless btrfs perhaps adds this
>> in the future?)
> not only "silent" single drive corruption problem but as I stated in start of topic - crash of first pair.

Bad things are going to happen if you loose a complete chunk of your 
filesystem.  I think the current state of the world is that you should 
assume that realistically you will be looking to your backups if you 
loose the wrong 2 disks in a raid1 or raid10 array.

However, the thing which worries me more with multidisk arrays is 
accidental disconnection of multiple disks, eg backplane fails, or a 
multi-lane connector is accidently unplugged.  Linux MD raid often seems 
to have the ability to reconstruct arrays after such accidents.  I don't 
have more recent experience with hardware controller arrays, but I have 
(sadly) found that such a situation is terminal on some older hardware 

Interested to hear other failure modes (and successful rescues) from 
RAID1+linear+XFS setups?


Ed W

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