On Thu, 2 Apr 2009, James Mansion wrote:
Might have to give the whole disk to ZFS with Solaris to give it confidence to enable write cache
Confidence, sure, but not necessarily performance at the same time. The ZFS Kool-Aid gets bitter sometimes too, and I worry that its reputation causes people to just trust it when they should be wary. If there's anything this thread does, I hope it helps demonstrate how easy it is to discover reality doesn't match expectations at all in this very messy area. Trust No One! Keep Your Laser Handy!
There's a summary of the expected happy ZFS actions at http://www.opensolaris.org/jive/thread.jspa?messageID=19264&; and a good cautionary tale of unhappy ZFS behavior in this area at http://blogs.digitar.com/jjww/2006/12/shenanigans-with-zfs-flushing-and-intelligent-arrays/ and its follow-up http://blogs.digitar.com/jjww/2007/10/back-in-the-sandbox-zfs-flushing-shenanigans-revisted/
Systems with a hardware write cache are pretty common on this list, which makes the situation described there not that unlikely to run into. The official word here is at
http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#FLUSH -- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
