From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Nelson Subject: Re: flashcache Date: Wed, 16 Jan 2013 15:55:13 -0600 Message-ID: <50F721C1.8070200@inktank.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f174.google.com ([209.85.223.174]:41588 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757037Ab3APVzL (ORCPT ); Wed, 16 Jan 2013 16:55:11 -0500 Received: by mail-ie0-f174.google.com with SMTP id c11so3554428ieb.33 for ; Wed, 16 Jan 2013 13:55:10 -0800 (PST) In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Sage Weil Cc: Gandalf Corvotempesta , ceph-devel@vger.kernel.org On 01/16/2013 03:46 PM, Sage Weil wrote: > On Wed, 16 Jan 2013, Gandalf Corvotempesta wrote: >> 2013/1/16 Sage Weil : >>> This sort of configuration effectively bundles the disk and SSD into a >>> single unit, where the failure of either results in the loss of both. >>> From Ceph's perspective, it doesn't matter if the thing it is sitting on >>> is a single disk, an SSD+disk flashcache thing, or a big RAID array. All >>> that changes is the probability of failure. >> >> Ok, it will fail, but this should not be an issue, in a cluster like >> ceph, right? >> With or without flashcache or SSD, ceph should be able to handle >> disks/nodes/osds failures on its own by replicating in real time to >> multiple server. > > Exactly. > >> Should I worry about loosing data in case of failure? It should >> rebalance automatically in case of failure with no data loss. > > You should not worry, except to the extent that 2 might fail > simultaneously, and failures in general are not good things. > >>> I would worry that there is a lot of stuff piling onto the SSD and it may >>> become your bottleneck. My guess is that another 1-2 SSDs will be a >>> better 'balance', but only experiementation will really tell us that. >>> >>> Otherwise, those seem to all be good things to put on teh SSD! >> >> I can't add more than 2 SSD, I don't have enough space. >> I can move OS to the first 2 spinning disks in raid1 software, if this >> will improve performance of SSD >> >> What about swap? I'm thinking to no use swap at all and start with >> 16/32GB RAM > > You could use the first (single) disk for os and logs. You might not even > bother with raid1, since you will presumably be replicating across hosts. > When the OSD disk dies, you can re-run your chef/juju/puppet rule or > whatever provisioning tool is at work to reinstall/configure the OS disk. > The data on the SSDs and data disks will all be intact. Other options might be network boot or even usb stick boot. > > sage > -- > 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 >