On Sun, November 4, 2007 4:32 pm, Timo Sirainen wrote:

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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.

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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.

Deliver’s 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. That’s pretty neat!