From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Smith Subject: Shrinking number of devices on a RAID-10 (near 2) array Date: Sat, 23 Aug 2014 16:31:10 +0000 Message-ID: <20140823163110.GE11855@bitfolk.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi, I am aware that for a very long time it was not possible to change the number of devices in an mdadm RAID-10. But then recently I am sure I saw threads here alluding to this being possible. e.g.: http://marc.info/?l=linux-raid&m=140768923829685&w=2 I have a 6 device RAID-10 near=2 array that I would like to shrink down to 4 devices. I have compiled mdadm 3.3.2 and am using kernel 3.16.0. $ sudo mdadm --detail /dev/md2 /dev/md2: Version : 0.90 Creation Time : Sun Jun 4 08:18:58 2006 Raid Level : raid10 Array Size : 471859200 (450.00 GiB 483.18 GB) Used Dev Size : 309363520 (295.03 GiB 316.79 GB) Raid Devices : 6 Total Devices : 6 Preferred Minor : 2 Persistence : Superblock is persistent Update Time : Sat Aug 23 15:23:38 2014 State : active Active Devices : 6 Working Devices : 6 Failed Devices : 0 Spare Devices : 0 Layout : near=2 Chunk Size : 64K UUID : 3905b303:ca604b72:be5949c4:ab051b7a Events : 0.312149991 Number Major Minor RaidDevice State 0 8 51 0 active sync /dev/sdd3 1 8 67 1 active sync /dev/sde3 2 8 83 2 active sync /dev/sdf3 3 8 19 3 active sync /dev/sdb3 4 8 35 4 active sync /dev/sdc3 5 8 3 5 active sync /dev/sda3 $ sudo ./mdadm --grow -n4 /dev/md2 --backup-file /var/tmp/mdadm.backup mdadm: Cannot set new_data_offset: RAID10 reshape not supported on this kernel Is that not yet possible, then? (Each device is 320GB so it should all fit with only four of them) Cheers, Andy