From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ted Ts'o Subject: Re: [Lsf-pc] [Topic] Bcache Date: Wed, 14 Mar 2012 14:54:56 -0400 Message-ID: <20120314185455.GD28042@thunk.org> References: <20120314133228.GA2284@dhcp-172-18-216-138.mtv.corp.google.com> <20120314155339.GC30235@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:58401 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755142Ab2CNSzC (ORCPT ); Wed, 14 Mar 2012 14:55:02 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: chetan loke Cc: Kent Overstreet , Vivek Goyal , lsf-pc@lists.linux-foundation.org, nauman@google.com, linux-scsi@vger.kernel.org, dm-devel@redhat.com On Wed, Mar 14, 2012 at 02:33:25PM -0400, chetan loke wrote: > But you are not explaining why dm is not the right stack. Just because > it crashed when you tried doesn't mean it's not the right place. > flash-cache works, doesn't it? flash-cache's limitation is because > it's a dm-target or because it is using hashing or something else? > There are start-ups who are doing quite great with SSD-cache+dm. So > please stop kidding yourself. SATA-attached flash is not the only kind of flash out there you know. There is also PCIe-attached flash which is a wee bit faster (where wee is defined as multiple orders of magnitude --- SATA-attached SSD's typically have thousands of IOPS; Fusion I/O is shipping product today with hundreds of thousands of IOPS, and has demonstrated a billion IOPS early this year). And Fusion I/O isn't the only company shipping PCIe-attached flash products. Startups may be doing great on SSD's; you may want to accept the fact that there is stuff which is way, way, way better out there than SSD's which are available on the market *today*. And it's not like bache which is a new project. It's working code, just like flash cache is today. So it's not like it needs to justify its existence. Best regards, - Ted