From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58589) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uq1Gg-0001ZA-8s for qemu-devel@nongnu.org; Fri, 21 Jun 2013 09:20:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Uq1Gb-0004Am-8i for qemu-devel@nongnu.org; Fri, 21 Jun 2013 09:20:46 -0400 Received: from mail-qa0-x236.google.com ([2607:f8b0:400d:c00::236]:57977) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Uq1Gb-0004Ag-4b for qemu-devel@nongnu.org; Fri, 21 Jun 2013 09:20:41 -0400 Received: by mail-qa0-f54.google.com with SMTP id n20so526383qaj.6 for ; Fri, 21 Jun 2013 06:20:40 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <7029962A8C6EFDBC98B51E44@nimrod.local> <20130411092548.GE8904@stefanha-thinkpad.redhat.com> <20130620094618.GC15672@stefanha-thinkpad.redhat.com> Date: Fri, 21 Jun 2013 15:20:40 +0200 Message-ID: From: Stefan Hajnoczi Content-Type: text/plain; charset=ISO-8859-1 Subject: Re: [Qemu-devel] Adding a persistent writeback cache to qemu List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Sage Weil Cc: Josh Durgin , qemu-devel , Alex Bligh On Thu, Jun 20, 2013 at 5:58 PM, Sage Weil wrote: > On Thu, 20 Jun 2013, Stefan Hajnoczi wrote: > I'm not really sure what the best path forward is. Putting the > functionality in qemu would benefit lots of other storage backends, > putting it in librbd would capture various other librbd users (xen, tgt, > and future users like hyper-v), and using new kernels works today but > creates a lot of friction for operations. If this is a common Ceph performance bottleneck, then librbd is a good place to put it. I believe you don't have to go over the external network with Gluster or pNFS if data is colocated on the same host, because they talk directly to the storage node. (There are probably configurations where this isn't possible though.) Stefan