We're running a Cyrus IMAP server on a T2000 under Solaris 10 with
about 1 TB of mailboxes on ZFS filesystems. Recently, when under
load, we've had incidents where IMAP operations became very slow. The
general symptoms are that the number of imapd, pop3d, and lmtpd
processes increases, the CPU load average increases, but the ZFS I/O
bandwidth decreases. At the same time, ZFS filesystem operations
become very slow. A rewrite of a small file can take two minutes.
We've added memory; this was an improvement, but the incidents
continued. The next step is to disable ZFS prefetch and test this
under load. If that doesn't help either, we're down to ZFS bugs.
Our incidents seem similar to the ones at UC Davis:
http://vpiet.ucdavis.edu/docs/EmailReviewCmte.Report_Feb2008.pdf
These were attributed to bug 6535160, but this one is fixed on our
server with patch 127127-11. Bug 6535172, ``zil_sync causing long
hold times on zl_lock'', doesn't have a patch yet:
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6535172
Could this bug cause our problem? How do I confirm that it does?
Is there a workaround?
Cyrus IMAP uses several moderate-sized databases that are
memory-mapped by all processes. I can move these from ZFS to UFS if
this is likely to help.
--
-Gary Mills- -Unix Support- -U of M Academic Computing and Networking-
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