Received: from maia.hub.org (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id 588506325E3 for ; Sat, 20 Feb 2010 19:16:48 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 96325-04 for ; Sat, 20 Feb 2010 23:16:31 +0000 (UTC) X-Greylist: delayed 00:09:15.649003 by SQLgrey-1.7.6 Received: from nyi.unixathome.org (nyi.unixathome.org [64.147.113.42]) by mail.postgresql.org (Postfix) with ESMTP id 75C3F632537 for ; Sat, 20 Feb 2010 19:16:37 -0400 (AST) Received: from localhost (localhost [127.0.0.1]) by nyi.unixathome.org (Postfix) with ESMTP id D9562508A8; Sat, 20 Feb 2010 23:07:19 +0000 (GMT) X-Virus-Scanned: amavisd-new at unixathome.org Received: from nyi.unixathome.org ([127.0.0.1]) by localhost (nyi.unixathome.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Qq2IteUODgK7; Sat, 20 Feb 2010 23:07:18 +0000 (GMT) Received: from smtp-auth.unixathome.org (smtp-auth.unixathome.org [10.4.7.7]) (Authenticated sender: hidden) by nyi.unixathome.org (Postfix) with ESMTPSA id AA26850843 ; Sat, 20 Feb 2010 23:07:18 +0000 (GMT) Message-ID: <4B806B24.40503@langille.org> Date: Sat, 20 Feb 2010 18:07:16 -0500 From: Dan Langille Organization: The FreeBSD Diary User-Agent: Thunderbird 2.0.0.23 (X11/20091018) MIME-Version: 1.0 To: Bruce Momjian CC: Matthew Wakeling , Greg Smith , Laszlo Nagy , pgsql-performance Subject: Re: SSD + RAID References: <201002201828.o1KIStQ12830@momjian.us> In-Reply-To: <201002201828.o1KIStQ12830@momjian.us> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-2.239 tagged_above=-10 required=5 tests=AWL=0.360, BAYES_00=-2.599 X-Spam-Level: X-Archive-Number: 201002/279 X-Sequence-Number: 37700 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Bruce Momjian wrote: > Matthew Wakeling wrote: >> On Fri, 13 Nov 2009, Greg Smith wrote: >>> In order for a drive to work reliably for database use such as for >>> PostgreSQL, it cannot have a volatile write cache. You either need a write >>> cache with a battery backup (and a UPS doesn't count), or to turn the cache >>> off. The SSD performance figures you've been looking at are with the drive's >>> write cache turned on, which means they're completely fictitious and >>> exaggerated upwards for your purposes. In the real world, that will result >>> in database corruption after a crash one day. >> Seagate are claiming to be on the ball with this one. >> >> http://www.theregister.co.uk/2009/12/08/seagate_pulsar_ssd/ > > I have updated our documentation to mention that even SSD drives often > have volatile write-back caches. Patch attached and applied. Hmmm. That got me thinking: consider ZFS and HDD with volatile cache. Do the characteristics of ZFS avoid this issue entirely? - -- Dan Langille BSDCan - The Technical BSD Conference : http://www.bsdcan.org/ PGCon - The PostgreSQL Conference: http://www.pgcon.org/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.13 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkuAayQACgkQCgsXFM/7nTyMggCgnZUbVzldxjp/nPo8EL1Nq6uG 6+IAoNGIB9x8/mwUQidjM9nnAADRbr9j =3RJi -----END PGP SIGNATURE-----