From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush Date: Mon, 23 Aug 2010 16:01:15 +0200 Message-ID: <4C727F2B.6060501@fusionio.com> References: <1281616891-5691-1-git-send-email-tj@kernel.org> <20100820132214.GA6184@lst.de> <4C6E9CAF.5010202@redhat.com> <4C7269E9.9070304@kernel.org> <20100823124815.GA20095@lst.de> <4C727E96.5020801@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4C727E96.5020801@redhat.com> Sender: linux-ide-owner@vger.kernel.org To: Ric Wheeler Cc: Christoph Hellwig , Tejun Heo , "linux-fsdevel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-ide@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-raid@vger.kernel.org" , "James.Bottomley@suse.de" , "tytso@mit.edu" , "chris.mason@oracle.com" , "swhiteho@redhat.com" , "konishi.ryusuke@lab.ntt.co.jp" , "dm-devel@redhat.com" , "vst@vlnb.net" , "jack@suse.cz" , "hare@suse.de" List-Id: dm-devel.ids On 2010-08-23 15:58, Ric Wheeler wrote: > On 08/23/2010 08:48 AM, Christoph Hellwig wrote: >> On Mon, Aug 23, 2010 at 02:30:33PM +0200, Tejun Heo wrote: >>> It might be useful to give several example configurations with >>> different cache configurations. I don't have much experience with >>> battery backed arrays but aren't they suppose to report write through >>> cache automatically? >> >> They usually do. I have one that doesn't, but SYNCHRONIZE CACHE on >> it is so fast that it effectively must be a no-op. >> > > Arrays are not a problem in general - they normally have internally, redundant > batteries to hold up the cache. > > The issue is when you have an internal hardware RAID card with a large cache. > Those cards sit in your server and the batteries on the card protect its > internal cache, but do not have the capacity to hold up the drives behind it. > > Normally, those drives should have their write cache disabled, but sometimes > (especially with S-ATA disks) this is not done. The problem purely exists on arrays that report write back cache enabled AND don't implement SYNC_CACHE as a noop. Do any of them exist, or are they purely urban legend? -- Jens Axboe