ZFS for Cyrus IMAP storage

Rudy Gevaert Rudy.Gevaert at UGent.be
Sat May 5 17:20:32 EDT 2007

Vincent Fox wrote:
> I originally brought up the ZFS question.
> We seem to have arrived at a similar solution after much 
> experimentation.  Meaning using ZFS for the things it does well already, 
> and  leveraging proven hardware to fill in the weak spots.
> I have a pair of Sun 3510FC arrays we have exported 2 RAID5 LUNs (5 
> disks each) with one on primary and the other on second controller. This 
> is to exploit the active-active controller feature of the 3510FC.  We 
> are also doing multipathing through a pair of SAN fabric switches.
> On top of that we then use ZFS to join a LUN from each array into a 
> mirror pair, and then add the other pair as well. I guess you could call 
> it RAID 5+1+0.  This architecture allows us to add more storage to the 
> pool while online, by adding more 3510FC array pairs to the pool.
> Performance in benchmarking (Bonnie++ etc.) has shown to be little 
> different from turning them into JBOD and doing everything with ZFS.   
> Behavior is more predictable to me since I know that the 3510 firmware 
> knows how to rebuild a RAID5 set using the assigned spare drive in that 
> array.  With ZFS I see no way to specify which disk is assigned as spare 
> to a particular set of disks, which could mean a spare is pulled from 
> another array.
> It's pretty nifty to be able to walk into the machine room and flip off 
> the power to an entire array and things keep working without a blip.  
> It's not the most efficient usage of disk space but with performance & 
> safety this promising for an EMAIL SERVER it will definitely be 
> welcome.  I dread the idea of silent data corruption or long fsck time 
> on a 1+ TB mail spool which ZFS should save us from.  I have atime=off 
> and compression=on.  Our setup is slightly different from yours in that 
> we are clustering 2  T2000 with 8GB RAM each, and we are currently 
> setting up Solaris Cluster 3.2 software in failover configuration so we 
> can patch without downtime.
> Thanks for the idea about daily snapshots for recovering recent data, I 
> like that idea a lot.  I'll tinker around with it I wonder if there'd be 
> much penalty to upping the snapshots to every 8 hours.  Depends on how 
> much churn there is in your mail spool I suppose.
> This system should move into production later this month.  We have 
> 70,000 accounts that we'll begin a long and slow migration from our 
> UW-IMAP pool of servers.  We have an existing Perdition proxy server 
> setup, which will allow us to migrate users transparently.  Hopefully 
> I'll have more good things to say about it sometime thereafter.

Are you going to do this with "1" perdition server?  Make sure you have 
compiled perdition with /dev/urandom, or an other sort of non blocking 
entropy providing device :)


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