From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: high throughput storage server? Date: Wed, 23 Feb 2011 16:15:50 +0100 Message-ID: References: <4D5EFDD6.1020504@hardwarefreak.com> <4D62DE55.8040705@hardwarefreak.com> <4D63BC6D.8010209@hardwarefreak.com> <4D64A082.9000601@hardwarefreak.com> <4D6518ED.1080908@anonymous.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4D6518ED.1080908@anonymous.org.uk> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 23/02/2011 15:25, John Robinson wrote: > On 23/02/2011 13:56, David Brown wrote: > [...] >> Incidentally, what's your opinion on a RAID1+5 or RAID1+6 setup, where >> you have a RAID5 or RAID6 build from RAID1 pairs? You get all the >> rebuild benefits of RAID1 or RAID10, such as simple and fast direct >> copies for rebuilds, and little performance degradation. But you also >> get multiple failure redundancy from the RAID5 or RAID6. It could be >> that it is excessive - that the extra redundancy is not worth the >> performance cost (you still have poor small write performance). > > I'd also be interested to hear what Stan and other experienced > large-array people think of RAID60. For example, elsewhere in this > thread Stan suggested using a 40-drive RAID-10 (i.e. a 20-way RAID-0 > stripe over RAID-1 pairs), and I wondered how a 40-drive RAID-60 (i.e. a > 10-way RAID-0 stripe over 4-way RAID-6 arrays) would perform, both in > normal and degraded situations, and whether it might be preferable since > it would avoid the single-disk-failure issue that the RAID-1 mirrors > potentially expose. My guess is that it ought to have similar random > read performance and about half the random write performance, which > might be a trade-off worth making. > Basically you are comparing a 4-drive RAID-6 to a 4-drive RAID-10. I think the RAID-10 will be faster for streamed reads, and a lot faster for small writes. You get improved safety in that you still have a one-drive redundancy after a drive has failed, but you pay for it in longer and more demanding rebuilds. But certainly RAID60 (or at least RAID50) seems to be a choice many raid controllers support, so it must be popular.