From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Sandeen Subject: Re: [PATCH] disable queue flag test in barrier check Date: Thu, 26 Jun 2008 09:57:18 -0500 Message-ID: <4863AE4E.5060908@sandeen.net> References: <486307EA.7080007@sandeen.net> <48635284.3060001@sgi.com> <486398B7.50306@sandeen.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: David Lethe Cc: Timothy Shimmin , xfs-oss , LinuxRaid , NeilBrown , jeremy@sgi.comwe List-Id: linux-raid.ids David Lethe wrote: > Fyi - related problem is seen with solaris & zfs when users attach them > to hardware-based RAID subsystems. The vendors had > to make firmware tweaks to address solaris's > flush-to-disk-after-all-writes. > > Not sure what you mean about non-volatile vs. volatile write cache, > however. If you want to see if write cache is enabled on a disk drive, > or > Even a logical disk on a hardware-based RAId, under Linux, then google > "mode page editor" for lots of choices. Also look up zfs write cache > raid and you'll get information that you can just as easily apply to > Linux implementations of md. I'm not so interested in whether it is enabled; I'd like to know if it is safe (to varying degrees) in the event of a power failure, and I don't think there's any way we can know that. So the administrator, if she's sure that all cached writes will hit disk even if a breaker pops, can disable barriers. If it's just a 32MB cache seagate drive plugged into the wall, you probably had better be sure barriers are enabled or you may well have a scrambled filesystem post-power-outage. -Eric