Extreme performance falling on ZFS by durable operation of a server

[Alexandr D. Sergeev]

Hi, all!

There are problems with a server on FreeBSD 7.2 CURRENT (6 Jul 2009), carrying out the task of mail server SMTP, IMAP.

Messages are stored in maildirs on file system ZFS (mirror of 2 SAS 3k drives).
Dovecot is used as IMAP server.

After reboot the system works perfectly, however, somewhere in a month, at the same load, arise periodic long delays at opening of new letters.

Judging by output iostat -x -w 1, during these moments the disk subsystem is strongly loaded.
%busy disks comes nearer to 100 %. Readings nearby 300 per sec prevail. and approx. 10MBytes per sec.

Somebody can advise, what diagnostics needed, for understanding of the reason of problems?

There is an opinion that a problem with ZFS.

Probably, it does not have enough memory. Because during the periods of occurrence of a problem,  ARC is have less 300MB:

vmstat -m
...
      solaris 1245732 274745K       - 25872717949  16,32,64,128,256,512,1024,2048,4096
...

Or it is bug of ZFS implementation.

--
Best regards,
Alexandr D.Sergeev