From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David C. Rankin" Subject: How best to re-sync raid1 array? zero superblock on removed disk and let it rebuild? Date: Fri, 28 Aug 2015 04:22:09 -0500 Message-ID: <55E02841.9050701@suddenlinkmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: mdraid List-Id: linux-raid.ids All, I had a disc-controller failure on a server running several raid1 arrays. The disks are fine, but I have had the root partition come up in degraded mode. What is the best way to tell mdraid to resync the disks? Here are the symptoms: # cat /proc/mdstat Personalities : [raid1] md1 : active raid1 sdb7[1] 52396032 blocks super 1.2 [2/1] [_U] md3 : active raid1 sdb6[1] sda6[0] 1047552 blocks super 1.2 [2/2] [UU] md2 : active raid1 sda8[0] sdb8[1] 922944192 blocks super 1.2 [2/2] [UU] bitmap: 0/7 pages [0KB], 65536KB chunk md0 : active raid1 sda5[0] sdb5[1] 204608 blocks super 1.2 [2/2] [UU] unused devices: # mdadm --misc --detail /dev/md1 /dev/md1: Version : 1.2 Creation Time : Wed Nov 27 04:35:49 2013 Raid Level : raid1 Array Size : 52396032 (49.97 GiB 53.65 GB) Used Dev Size : 52396032 (49.97 GiB 53.65 GB) Raid Devices : 2 Total Devices : 1 Persistence : Superblock is persistent Update Time : Fri Aug 28 04:12:18 2015 State : clean, degraded Active Devices : 1 Working Devices : 1 Failed Devices : 0 Spare Devices : 0 Name : archiso:1 UUID : 320d86f7:22999af5:5eeefee1:35cd8970 Events : 100308 Number Major Minor RaidDevice State 0 0 0 0 removed 1 8 23 1 active sync /dev/sdb7 Reading, it looks like one approach is the boot the install media and then zero the superblock on /dev/sda7 and then reboot. Will that force a rebuild, or do I need to fail and remove the disk first? I was thinking: # mdadm --zero-superblock /dev/sda7 should set it up for a rebuild without more. Is this a sane approach? -- David C. Rankin, J.D.,P.E.