[Dovecot] XFS vs EXT4 for mail storage

[Stan Hoeppner]

On 5/3/2013 9:21 AM, Charles Marcus wrote:
> On 2013-05-03 8:34 AM, Stan Hoeppner <stan at hardwarefreak.com> wrote:
>> I assume /var will hold user mail dirs.
> 
> Yes, in /var/vmail
> 
>> Do /var/ and /snaps reside on the same RAID array, physical disks?
> 
> Yes - vmware host is a Dell R515, with ESXi installed to mirrored
> internal SATA drives, with 8 drives in RAID 10 for all of the VMs. All
> storage is this local storage (no SAN/NAS).

Your RAID10 is on a PERC correct?  You have four 7.2K SATA stripe
spindles.  Do you mind posting the RAID10 strip/chunk size?  The RAID
geometry can be critical, not just for mail, but your entire VM setup.
Also, what's your mdbox max file size?

>> How about the other filesystems I snipped? If you have a large number
>> of filesystems atop the same RAID, some of them being XFS, this could
>> create a head thrashing problem under high load increasing latency and
>> thus response times.
> 
> Ouch...

Don't fret yet.

> This ESXi host also hosts 2 server 2008R2 vms...

So, what, 3 production VMs total?  That shouldn't be a problem,
unless... (read below)

>> Would you mind posting: ~$ xfs_info /dev/vg/var

> meta-data=/dev/mapper/vg-var     isize=256    agcount=4, agsize=45875200
...
> meta-data=/dev/mapper/vg-snaps   isize=256    agcount=4, agsize=262144 blks

Ok, good, mkfs gave you 4 AGs per filesystem, 8 between the two.  This
shouldn't be a problem.

However, ISTR you mentioning that your users transfer multi-GB files, up
to 50GB, on a somewhat regular basis, to/from the file server over GbE
at ~80-100MB/s.  If these big copies hit the same 4 RAID10 spindles it
may tend to decrease IMAP response times due to seek contention.  This
has nothing to do with XFS.  It's the nature of shared storage.

> Thanks again Stan...

You bet.

-- 
Stan