From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush Date: Mon, 23 Aug 2010 14:30:33 +0200 Message-ID: <4C7269E9.9070304@kernel.org> References: <1281616891-5691-1-git-send-email-tj@kernel.org> <20100820132214.GA6184@lst.de> <4C6E9CAF.5010202@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , jaxboe@fusionio.com, 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 To: Ric Wheeler Return-path: In-Reply-To: <4C6E9CAF.5010202@redhat.com> Sender: linux-raid-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hello, On 08/20/2010 05:18 PM, Ric Wheeler wrote: > On 08/20/2010 09:22 AM, Christoph Hellwig wrote: >> FYI: here's a little writeup to document the new cache flushing scheme, >> intended to replace Documentation/block/barriers.txt. Any good >> suggestion for a filename in the kernel tree? >> > > I was thinking that we might be better off using the "durable > writes" term more since it is well documented (at least in the > database world, where it is the "D" in ACID properties). Maybe > "durable_writes_support.txt" ? The term is very foreign to people outside of enterprise / database loop. writeback-cache.txt or write-cache-control.txt sounds good enough to me. >> The Linux block layer provides a two simple mechanism that lets filesystems >> control the caching behavior of the storage device. These mechanisms are >> a forced cache flush, and the Force Unit Access (FUA) flag for requests. >> > > Should we mention that users can also disable the write cache on the > target device? > > It might also be worth mentioning that storage needs to be properly > configured - i.e., an internal hardware RAID card with battery > backing needs can expose itself as a writethrough cache *only if* it > actually has control over all of the backend disks and can > flush/disable their write caches. 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? Thanks. -- tejun