From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Sandeen Subject: Re: RAID needs more to survive a power hit, different /boot layout for example (was Re: draft howto on making raids for surviving a disk crash) Date: Mon, 04 Feb 2008 08:25:37 -0600 Message-ID: <47A72061.3010800@sandeen.net> References: <47A612BE.5050707@pobox.com> <47A623EE.4050305@msgid.tls.msk.ru> <47A62A17.70101@pobox.com> <47A6DA81.3030008@msgid.tls.msk.ru> <47A6EFCF.9080906@pobox.com> <47A7188A.4070005@msgid.tls.msk.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com To: Justin Piszcz Cc: Michael Tokarev , Moshe Yudkowsky , linux-raid@vger.kernel.org, xfs@oss.sgi.com List-Id: linux-raid.ids Justin Piszcz wrote: > Why avoid XFS entirely? > > esandeen, any comments here? Heh; well, it's the meme. see: http://oss.sgi.com/projects/xfs/faq.html#nulls and note that recent fixes have been made in this area (also noted in the faq) Also - the above all assumes that when a drive says it's written/flushed data, that it truly has. Modern write-caching drives can wreak havoc with any journaling filesystem, so that's one good reason for a UPS. If the drive claims to have metadata safe on disk but actually does not, and you lose power, the data claimed safe will evaporate, there's not much the fs can do. IO write barriers address this by forcing the drive to flush order-critical data before continuing; xfs has them on by default, although they are tested at mount time and if you have something in between xfs and the disks which does not support barriers (i.e. lvm...) then they are disabled again, with a notice in the logs. Note also that ext3 has the barrier option as well, but it is not enabled by default due to performance concerns. Barriers also affect xfs performance, but enabling them in the non-battery-backed-write-cache scenario is the right thing to do for filesystem integrity. -Eric > Justin. >