On 22 Jul 2014, at 04:57, Murray Trainer mtrainer@westnet.com.au wrote:
We have a couple of dovecot director proxies and six backed mailstores each accessing mailboxes stored on five NFSv4 filsystems with about 1TB of mail on each in maildir format. We have about 800 max users on each mailstore at peak times and performance appears to starting to degrade at these times. The mailstores are pretty recent hardware with 64GB of RAM and 24 cores. The NFS storage is EMC VNX and we are doing about 250 I/O per sec upto max of 500 on each filesystem. I need to squeeze more performance out of these servers whether that is in the NFS client, Dovecot or Linux OS/kernel areas. We use LDAP for auth and I am doing some tuning in that area. The NFS filesystems are mounted with the options below:
10.11.0.238:/mailbox_store_01 on /home1 type nfs4 (rw,relatime,vers=4.0,rsize=65536,wsize=65536,namlen=255,hard,nordirplus,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=10.11.0.96,local_lock=none,addr=10.11.0.238)
Does relatime work with NFS? If yes, changing it to noatime would save some I/O.
maildir_very_dirty_syncs=yes should be helpful.
# 2.2.9: /etc/dovecot/dovecot.conf
mailbox_list_index=yes might be useful, although it has had some further performance improvements since v2.2.13. I should try to make v2.2.14 soon..
quota = maildir
Dict file quota would be a bit faster than maildir++ quota.