From mboxrd@z Thu Jan 1 00:00:00 1970 From: Reindl Harald Subject: Re: proactive disk replacement Date: Tue, 21 Mar 2017 14:24:08 +0100 Message-ID: <09f4c794-8b17-05f5-10b7-6a3fa515bfa9@thelounge.net> References: <3FA2E00F-B107-4F3C-A9D3-A10CA5F81EC0@allygray.2y.net> <11c21a22-4bbf-7b16-5e64-8932be768c68@websitemanagers.com.au> <02316742-3887-b811-3c77-aad29cda4077@websitemanagers.com.au> <583576ca-a76c-3901-c196-6083791533ee@thelounge.net> <58D126EB.7060707@hesbynett.no> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <58D126EB.7060707@hesbynett.no> Sender: linux-raid-owner@vger.kernel.org To: David Brown , Adam Goryachev , Jeff Allison Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Am 21.03.2017 um 14:13 schrieb David Brown: > On 21/03/17 12:03, Reindl Harald wrote: >> >> Am 21.03.2017 um 11:54 schrieb Adam Goryachev: > >> >>> In addition, you claim that a drive larger than 2TB is almost certainly >>> going to suffer from a URE during recovery, yet this is exactly the >>> situation you will be in when trying to recover a RAID10 with member >>> devices 2TB or larger. A single URE on the surviving portion of the >>> RAID1 will cause you to lose the entire RAID10 array. On the other hand, >>> 3 URE's on the three remaining members of the RAID6 will not cause more >>> than a hiccup (as long as no more than one URE on the same stripe, which >>> I would argue is ... exceptionally unlikely). >> >> given that when your disks have the same age errors on another disk >> become more likely when one failed and the heavy disk IO due recovery of >> a RAID6 with takes *many hours* where you have heavy IO on *all disks* >> compared with a way faster restore of RAID1/10 guess in which case a URE >> is more likely >> >> additionally why should the whole array fail just because a single block >> get lost? the is no parity which needs to be calculated, you just lost a >> single block somewhere - RAID1/10 are way easier in their implementation > > If you have RAID1, and you have an URE, then the data can be recovered > from the other have of that RAID1 pair. If you have had a disk failure > (manual for replacement, or a real failure), and you get an URE on the > other half of that pair, then you lose data. > > With RAID6, you need an additional failure (either another full disk > failure or an URE in the /same/ stripe) to lose data. RAID6 has higher > redundancy than two-way RAID1 - of this there is /no/ doubt yes, but with RAID5/RAID6 *all disks* are involved in the rebuild, with a 10 disk RAID10 only one disk needs to be read and the data written to the new one - all other disks are not involved in the resync at all for most arrays the disks have a similar age and usage pattern, so when the first one fails it becomes likely that it don't take too long for another one and so load and recovery time matters