[Dovecot] XFS vs EXT4 for mail storage

[Charles Marcus]

On 2013-05-03 11:10 PM, Stan Hoeppner <stan at hardwarefreak.com> wrote:
> 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?

Correct... it is a PERC H700 (integrated)

> You have four 7.2K SATA stripe spindles.

Actually, no, I have 6 15k 450G SAS6G hard drives (Seagate Cheetah 
ST3450857SS) in this RAID10 array...

:)

> Do you mind posting the RAID10 strip/chunk size? The RAID geometry can be critical, not just for mail, but your entire VM setup.

I just used the defaults when I created it (crossing fingers hoping that 
wasn't a huge mistake). But - I'm not sure how to provide the answer to 
the question (is my ignorance showing yet?)...

>   Also, what's your mdbox max file size?

Haven't settled on that yet. I was thinking of using the defaults there 
too. I try to stay with defaults whenever possible, especially if I 
don't know enough to know why I would want to change something.

>>> 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.

Cool...

> 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.

I think you're confusing me/us with someone else. This is definitely not 
something our users do, not even close. We do deal with a lot of large 
email attachments though. I used to have a max size of 50MB, but reduced 
it to 25MB about 8 months ago (equivalent of google's max size)...

So, looks like I'm fine with what I have now...

Thanks again,

-- 

Best regards,

Charles