From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wido den Hollander Subject: Re: ceph for small cluster? Date: Wed, 02 Jan 2013 13:17:14 +0100 Message-ID: <50E4254A.5000502@widodh.nl> References: <50E0B457.70200@meetinghouse.net> <50E19DC5.303@meetinghouse.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from smtp02.mail.pcextreme.nl ([109.72.87.138]:50657 "EHLO smtp02.mail.pcextreme.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752667Ab3ABMRR (ORCPT ); Wed, 2 Jan 2013 07:17:17 -0500 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Matthew Roy Cc: Miles Fidelman , ceph-devel On 01/01/2013 01:13 AM, Matthew Roy wrote: > On Mon, Dec 31, 2012 at 9:14 AM, Miles Fidelman > wrote: >> >> >> Which raises another question: how are you combining drives within each OSD (raid, lvm, ?). >> > > I'm not combining them, just running an OSD per data disk. On this > cluster it's 2 disks for each of the 3 nodes. I ended up that way > only because I added the second disk to each node after getting > started. There was an inktank blog post not too long ago about the > performance of RAID'ed disks on OSDs that might provide quantitative > justification for which route to go. > > Like Wido suggests, I also use a shared SSD for journal on each node. > The journal's not really about speeding recovery from failed > OSDs/disks, it's about being able to ACK writes faster and still > retain integrity when Bad Things happen. If you're RAIDing with a > battery-backed cache I think you can run without a journal, but I > don't know the details on that. > That depends on the RAID controller. Some (like Areca I think) cache O_DIRECT writes in their write cache, but other still flush them directly to the disks although they have a cache with BBU. I'd try to prevent using any RAID system with Ceph. Let the replication handle everything. The less hardware and complexity you add, the less can fail. Wido > Matthew > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >