From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stan Hoeppner Subject: Re: Suboptimal raid6 linear read speed Date: Fri, 18 Jan 2013 02:31:19 -0600 Message-ID: <50F90857.3010305@hardwarefreak.com> References: <20130115123301.GA11948@rabbit.us> <50F55046.7050605@turmel.org> <20130115125507.GA12184@rabbit.us> <50F614F7.20104@hardwarefreak.com> <20130116025857.GA31112@rabbit.us> <50F70DB7.6020104@hardwarefreak.com> Reply-To: stan@hardwarefreak.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mikael Abrahamsson Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 1/17/2013 9:51 AM, Mikael Abrahamsson wrote: > The probability of getting struck by lightning is a lot less than being > struck by a read error when rebuilding from the only remaining mirror > when one drive failed and you've replaced it. The probability of a URE during rebuild increases with the number and size of the source drives being read to rebuild the failed drive. Thus the probability of encountering a URE in the 1:1 drive scenario is extremely low, close to zero if you believe manufacturer specs. > > is applicable to RAID1 and RAID10 as well as RAID5. In Robin's example we're reading 12TB of sectors from 6 drives to complete the rebuild of one failed drive, so the overall probably of a URE is less than that of a single drive. With RAID1/10 we're only reading 2TB, well below the URE rates for single drives. So, no, the "URE scare" being propagated these days doesn't affect RAID1/10. If/when individual drive capacities exceed 10TB in the future, and if at that time the URE rates per drive do not improve, -then- this phenomenon will affect RAID1/10. But it does not currently with today's drives. -- Stan