Received: from localhost (unknown [200.46.204.183]) by mail.postgresql.org (Postfix) with ESMTP id AFB55640374 for ; Fri, 3 Apr 2009 06:53:37 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 58572-03-7 for ; Fri, 3 Apr 2009 06:53:35 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from westnet.com (westnet.com [216.187.52.2]) by mail.postgresql.org (Postfix) with ESMTP id 22E1A63EB26 for ; Fri, 3 Apr 2009 06:53:33 -0300 (ADT) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id n339rPCt008756; Fri, 3 Apr 2009 05:53:25 -0400 (EDT) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id n339rPur008752; Fri, 3 Apr 2009 05:53:25 -0400 (EDT) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Fri, 3 Apr 2009 05:53:25 -0400 (EDT) From: Greg Smith X-X-Sender: gsmith@westnet.com To: James Mansion cc: Scott Carey , Stef Telford , Mark Kirkwood , pgsql-performance@postgresql.org Subject: Re: Raid 10 chunksize In-Reply-To: <49D50F0E.6050807@mansionfamily.plus.com> Message-ID: References: <49D50F0E.6050807@mansionfamily.plus.com> User-Agent: Alpine 2.01 (GSO 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests=none X-Spam-Level: X-Archive-Number: 200904/55 X-Sequence-Number: 33422 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@gregsmith.com http://www.gregsmith.com Baltimore, MD