From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Sat, 29 Jul 2006 20:53:30 -0700 (PDT) Received: from sandeen.net (sandeen.net [209.173.210.139]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id k6U3rKDW031248 for ; Sat, 29 Jul 2006 20:53:20 -0700 Message-ID: <44CC2D1A.3060805@sandeen.net> Date: Sat, 29 Jul 2006 22:52:58 -0500 From: Eric Sandeen MIME-Version: 1.0 Subject: Re: write back cache and barriers References: <5545990.post@talk.nabble.com> In-Reply-To: <5545990.post@talk.nabble.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-To: xfs-bounce@oss.sgi.com List-Id: xfs To: calembour Cc: xfs@oss.sgi.com calembour wrote: > Hi, > I don't have a deep knowledge about filesystems and I've few experiences > with > raid configuration, so I need someone who can answer some questions about > write back cache and barriers. > > I have two sata hd (sda, sdb) configured in bios-raid 0 and relative device > created by dmraid on boot (nvidia_ihfaaicb). > > (1) what should I do to know if the write back cache is enabled or not ? lots of this is in the faq: http://oss.sgi.com/projects/xfs/faq.html#wcache > (2) if the write cache is enabled on both sda and sdb this mean that is > enabled > also on the raid device (/dev/mapper/nvidia_ihfaaicb) ? I'd guess that if there's a write cache anywhere under your device, then in effect the raid device would be considered write-cached. > (3) how should I do to enable/disable the write cache on the raid device ? see faq > If I try mounting a xfs filesystem I get a message like "barriers are not > supported by this device" but if I mount a ext3 or a reiserfs filesystem > respectively with options barrier=1 and barrier=flush they don't complain. > If I mount the reiserfs I explicity get a message like "using barriers". > So who tells the truth ?? I don't see ext3 or reiser actually checking whether the underlying device supports barriers. xfs does, in xfs_mountfs_check_barriers(). > (4) is there a way to know if the raid device supports barrier or not ? I'm not sure how barriers interact with multiple devices; perhaps someone else can answer.... > (5) is there a (not dangerous) test I can do to figure out if barriers are > really enabled and used with ext3 and reiserfs filesystems ? Dunno :) -Eric > Thanks for reading the message > Marco