On Dec 18, 2009, at 4:42 PM, Brandon Davidson wrote:

The Wiki article on NFS states that 1.1 and newer will flush attribute caches if necessary with mail_nfs_storage=yes. We're running 1.2.8 with that set, as well as mail_nfs_index=yes, mmap_disable=yes and fsync_disable=no. We have a pool of POP/IMAP and SMTP machines that are accessing the maildirs, and can't guarantee any sort of user session affinity to a particular host.

We also mount our NFS shares with 'noac', which is what I'm writing to ask about. I'd like to stop doing that for performance reasons. Do you see any issues with taking that out of the mount options, given our environment?

Dovecot's NFS cache flushing doesn't work perfectly. But I think some/most/all of those conditions exist also when attribute cache is disabled. Or maybe not. I can't really remember anymore what I read in the kernel code :) And that was only for Linux and FreeBSD, don't know about other OSes. The issue was about directory entry caching, I don't remember if attribute cache also disabled it.

Anyway.. I think you should just try enabling attribute cache and if things start breaking more, disable it again.