On Sun, November 4, 2007 4:32 pm, Timo Sirainen wrote: >> >> I didn't know that mail_nfs_index=yes resulted in a forced chown. >> How come that's necessary with NFS but not on local disks? >> > > It's used to flush NFS attribute cache. Enabling it allows you to use > multiple servers to access the same maildir at the same time while still > having attribute cache enabled (v1.0 required actime=0). If you don't need > this (and it's better if you don't), then just set the mail_nfs_* to "no" > and it works faster. > >> By the way I misinformed you about fsync_disable=yes. >> It was like that before i upgraded to v1.1, but v1.1 requires >> fsync_disable=no when mail_nfs_index=true so I had to disable it. > > So you use ZFS on the NFS server, but Dovecot is using NFS on client > side? The fsyncs then just mean that the data is sent to NFS server, not a > real fsync on ZFS. >
Thanks a lot for the help - this changed a lot! Dist writes fell to about 1/3 of before. I guess the reason is that ZFS can now make use if it's caching capabilities. Delivers activity is completely random since it's impossible to load balance a connection based on the e-mail recipient, since only the ip is known at the load balancing point. Therefore I have fsync_disable=no for deliver. It's easy to force the clients using imap/pop3 to the same server since it can be based on the ip only. Therefore I have fsync_disable=yes for imap/pop3. This changed everything. Now there's a real performance gain upgrading from 1.0.x to 1.1.x. About two or three times less disk activity overall (reads were already improved) for both reads and writes. Thats pretty neat!