Hi,
We experience serious performance problem with courier-imap with mail
stored in maildir format on NFS.
We have about 60 clients in total, which should not be a problematic number.
Here are the symptoms:
After some time, the load on the server gets high, though no single process
exhausts cpu and lots of memory are still available (most memory is used
for cache).
Access to the mails become horribly slow. Even an ls on the maildir is slow.
Restarting courier-imap gets things going again, but we just start a new
cycle and after some time we get slow performance again.
/home is mounted as nfs from one server, and /mnt/pmail is mounted as nfs
from another server, with Maildir in /home being a softlink to /mnt/pmail,
as illustrated is for user raph:
/home/raph/mail/Maildir->/mnt/pmail/home/rb/Maildir
Both servers export the filesystems with options
(rw,sync,no_root_squash,mp), and option nu_subtree_check is a default.
As mentioned above, an ls on /mnt/pmail becomes slow, on /home it's ok.
A server running exim mount the exact same directories, and there the
performance is fine. An ls on /mnt/pmail is fast, at the same time that the
same ls is slow in the server running courier-imap.
The install is old, and we introduced the use of NFS (in a kvm domain) to
ease upgrades. But we'd rather fix the problems without upgrading the whole
system for now (no need risking to introduce more problems without fixing
those we currently have).
This is on debian 5, courier-imap 4.4.0, nfs-common 1.1.2.
So, any and all advice on improving the solution is welcome! (NFS config,
courier config, etc)
Thanks in advance!
Raphaël
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