[Dovecot] Dovecot tuning for GFS2

[Jan-Frode Myklebust]

On Wed, Aug 21, 2013 at 02:18:52PM +0200, Andrea gabellini - SC wrote:
> 
> So you are using the same config I'm testing. I forgot to write that I
> use maildir.

I would strongly suggest using mdbox instead. AFAIK clusterfs' aren't
very good at handling many small files. It's a worst case random I/O 
usage pattern, with high rate of metadata operations on top.

We use IBM GPFS for clusterfs, and have finally completed the conversion
of a 130+ million inode maildir filesystem, into a 18 million inode mdbox
filesystem. I have no hard performance data showing the difference
between maildir/mdbox, but at a minimum mdbox is much easier to manage.
Backup of 130+ million files is painfull.. and also it feels nice to be
able do schedule batches of mailbox purges to off-hours, instead of doing
them at peak hours.

As for your settings, we use:

	mmap_disable = yes	# GPFS also support cluster-wide mmap, but for some reason we've disabled it in dovecot..
	mail_fsync = optimized
	mail_nfs_storage = no
	mail_nfs_index = no
	lock_method = fcntl

and of course Dovecot Director in front of them..



  -jf