dovecot - Jan 2011 - dovecot Digest, Vol 93, Issue 41

> From: Stan Hoeppner <stan at hardwarefreak.com>
 > Subject: Re: [Dovecot] SSD drives are really fast running Dovecot
 >
 >
 > Yes.  Go with a cluster filesystem such as OCFS or GFS2 and an 
inexpensive SAN
 > storage unit that supports mixed SSD and spinning storage such as the 
Nexsan
 > SATABoy with 2GB cache:  http://www.nexsan.com/sataboy.php

I can't speak for OCFS2, but after several years' experience with the 
filesystem I strongly recommend NOT using GFS/GFS2. Its locking model is 
incredibly slow (500 locks/second on a filesystem mounted with quotas 
enabled and noatime) and results in dire performance - plus there's a 
known crash vulnerability if files are repeatedly renamed in large 
directories (this bites us regularly...)

GFS2 isn't an "enterprise" filesystem by any stretch of the
imagination,
despite what a number of enthusiastic salespeople might try to convince 
you of. We're lucky to keep the GFS servers up for more than a week at a 
time.

Quoting Alan Brown <ajb2 at mssl.ucl.ac.uk>:
> I can't speak for OCFS2, but after several years' experience with  
> the filesystem I strongly recommend NOT using GFS/GFS2.
GFS2 works for me.  GFS was a bit slow, but GFS2 meets my (perhaps low)
needs.  Of course, my use case is different (e.g., I don't use it with
quotas, in fact I've stayed away from it anywhere I need quotas).
> Its locking model is incredibly slow (500 locks/second on a  
> filesystem mounted with quotas enabled and noatime) and results in  
> dire performance - plus
Did you raise plock_rate_limit from its defaults?  The defaults will
indeed suck.
> there's a known crash vulnerability if files are repeatedly renamed  
> in large directories (this bites us regularly...)
Never had that happen...  But then, my applications don't repeatedly
rename files in large directories (e.g., I don't use maildir) and I
don't use quotas on GFS.
> GFS2 isn't an "enterprise" filesystem by any stretch of the  
> imagination, despite what a number of enthusiastic salespeople might  
> try to convince you of. We're lucky to keep the GFS servers up for  
> more than a week at a time.
GFS isn't for all applications.  I've used it for 2 different
applications
for which it has proven well suited.  Every discussion I've seen about
GFS has always said "don't use it with large directories of small
files"
so if that is your use case, then you must be ignoring common wisdom...

Given the right use case (including dovecot with mbox and dovecot indexes)
it seems to work fine...  I've used it for another project also without
problems (been running for years now in both cases).

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

Go Longhorns!

Alan Brown put forth on 1/18/2011 10:22 AM:
>> From: Stan Hoeppner <stan at hardwarefreak.com>
>> Subject: Re: [Dovecot] SSD drives are really fast running Dovecot
>>
>>
>> Yes.  Go with a cluster filesystem such as OCFS or GFS2 and an
inexpensive SAN
>> storage unit that supports mixed SSD and spinning storage such as the
Nexsan
>> SATABoy with 2GB cache:  http://www.nexsan.com/sataboy.php
> 
> I can't speak for OCFS2, but after several years' experience with
the filesystem
> I strongly recommend NOT using GFS/GFS2. Its locking model is incredibly
slow
> (500 locks/second on a filesystem mounted with quotas enabled and noatime)
and
> results in dire performance - plus there's a known crash vulnerability
if files
> are repeatedly renamed in large directories (this bites us regularly...)
> 
> GFS2 isn't an "enterprise" filesystem by any stretch of the
imagination, despite
> what a number of enthusiastic salespeople might try to convince you of.
We're
> lucky to keep the GFS servers up for more than a week at a time.
What reliable performant cluster filesystem would you recommend Alan?  Or would
you recommend NFS instead?  NetApp?  BlueArc?

-- 
Stan