Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755398AbZICNvy (ORCPT ); Thu, 3 Sep 2009 09:51:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754016AbZICNvx (ORCPT ); Thu, 3 Sep 2009 09:51:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1648 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753438AbZICNvw (ORCPT ); Thu, 3 Sep 2009 09:51:52 -0400 Message-ID: <4A9FC9B3.1080809@redhat.com> Date: Thu, 03 Sep 2009 09:50:43 -0400 From: Ric Wheeler User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.1) Gecko/20090814 Fedora/3.0-2.6.b3.fc11 Lightning/1.0pre Thunderbird/3.0b3 MIME-Version: 1.0 To: Krzysztof Halasa CC: Christoph Hellwig , Mark Lord , Michael Tokarev , david@lang.hm, Pavel Machek , Theodore Tso , NeilBrown , Rob Landley , Florian Weimer , Goswin von Brederlow , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, corbet@lwn.net Subject: Re: raid is dangerous but that's secret (was Re: [patch] ext2/3: document conditions when reliable operation is possible) References: <20090828064449.GA27528@elf.ucw.cz> <20090828120854.GA8153@mit.edu> <20090830075135.GA1874@ucw.cz> <4A9A88B6.9050902@redhat.com> <4A9A9034.8000703@msgid.tls.msk.ru> <20090830163513.GA25899@infradead.org> <4A9BCCEF.7010402@redhat.com> <20090831131626.GA17325@infradead.org> <4A9BCDFE.50008@rtr.ca> <20090831132139.GA5425@infradead.org> <4A9F230F.40707@redhat.com> <4A9FA5F2.9090704@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1526 Lines: 41 On 09/03/2009 09:34 AM, Krzysztof Halasa wrote: > Ric Wheeler writes: > >>>> Just to add some support to this, all of the external RAID arrays that >>>> I know of normally run with write cache disabled on the component >>>> drives. >>> >>> Do they use "off the shelf" SATA (or PATA) disks, and if so, which ones? >> >> Which drives various vendors ships changes with specific products. >> Usually, they ship drives that have carefully vetted firmware, etc. >> but they are close to the same drives you buy on the open market. > > But they aren't the same, are they? If they are not, the fact they can > run well with the write-through cache doesn't mean the off-the-shelf > ones can do as well. Storage vendors have a wide range of options, but what you get today is a collection of s-ata (not much any more), sas or fc. Some times they will have different firmware, other times it is the same. > > Are they SATA (or PATA) at all? SCSI etc. are usually different > animals, though there are SCSI and SATA models which differ only in > electronics. > > Do you have battery-backed write-back RAID cache (which acknowledges > flushes before the data is written out to disks)? PC can't do that. We (red hat) have all kinds of different raid boxes... ric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/