From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: cache_mode none Date: Thu, 4 Oct 2012 12:53:59 -0700 Message-ID: <20121004195359.GC29494@google.com> References: <20121004102406.GC17229@narnia.kingsly.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20121004102406.GC17229-Z3X8UqLNtc1Swagx7F3lBaxOck334EZe@public.gmane.org> Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org On Thu, Oct 04, 2012 at 03:54:06PM +0530, Kingsly John wrote: > Hi! > > I've been trying out bcache over the last couple of weeks and couldn't find > this explained anywhere. > > On my setup here while writing with cache_mode set to none, there's a > near constant 30-40kb/sec write happening to the flash device all through. > But in the other modes the amount of data written is significantly > higher.(While copying the same set of files into a freshly formatted bcache > device) > > Does setting cache_mode to none just disable the cache for reading or does it > disable it for both reading and writing? > > If it's only disabled for reads, then with cache_mode set to none would > bcache still recover from an unclean shutdown? In cache_mode none, nothing new will be added to the cache (neither from writes nor cache misses), but the cache is still kept consistent - that's the reason for the writing that still happens to the flash devices, it's invalidating the cache whenever you do a write. It will still read from the cache, because there might still be dirty data in the cache.