From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Thornber Subject: Re: Performance Comparison among EnhanceIO, bcache and dm-cache. Date: Mon, 17 Jun 2013 11:29:44 +0100 Message-ID: <20130617102943.GA11121@debian> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: OS Engineering Cc: "koverstreet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org" , "linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , LKML , Jens Axboe , Padmini Balasubramaniyan , Amit Phansalkar List-Id: linux-bcache@vger.kernel.org On Tue, Jun 11, 2013 at 03:05:07PM +0000, OS Engineering wrote: ... > Dm-cache commits on-disk metadata every time a REQ_SYNC or REQ_FUA > bio is written. If no such requests are made then it commits > metadata once every second. If power is lost, it may lose some > recent writes. Not true (though it is true for thinp, which may be where you got this idea?). For caching we have to commit whenever data is moved about, otherwise a crash could result in us reading data that is not just out of date (acceptable for some), but used to belong to a totally different part of the device (always unacceptable). - Joe