From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hughes Subject: Dumb questions about mdadm #1 - replacing broken disks - "slot" reuse? Date: Fri, 18 Sep 2009 14:13:44 +0200 Message-ID: <4AB37978.5030403@Calva.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: linux-raid List-Id: linux-raid.ids mdadm version 2.6.7.2-3 on Debian Lenny, kernel 2.6.26-2-xen-amd64 I'm new to mdadm, all my experience with software raid/volume management type systems has been with Vertas VxVM on UnixWare. I'm replacing an existing UnixWare system by Linux and I'm trying to get a feel for how to perform some simple operations. As I understand it to replace a failed disk (assuming no hot spares for the moment) I just do: mdadm --manage /dev/md0 --remove /dev/failed-disk mdadm --manage /dev/md0 --add /dev/new-disk This works, but when I look at the results it looks rather ugly, the new disk goes in a new "slot" in the raid superblock. Is it the case that every time I replace a disk I'm going to get a new slot? Doesn't that make the raid "superblock" grow without limit? Before: # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 sdw[11] sdg[10] sdv[9] sdf[8] sdu[7] sde[6] sdt[5] sdd[4] sds[3] sdc[2] sdr[1] sdb[0] 426970368 blocks super 1.2 64K chunks 2 near-copies [12/12] [UUUUUUUUUUUU] bitmap: 1/204 pages [4KB], 1024KB chunk unused devices: # mdadm --examine /dev/sdb: Magic : a92b4efc Version : 1.2 Feature Map : 0x1 Array UUID : 9477b121:204de4c4:a96d58e9:85746699 Name : caronia:testarray2 (local to host caronia) Creation Time : Fri Sep 18 12:59:24 2009 Raid Level : raid10 Raid Devices : 12 Avail Dev Size : 142323568 (67.87 GiB 72.87 GB) Array Size : 853940736 (407.19 GiB 437.22 GB) Used Dev Size : 142323456 (67.87 GiB 72.87 GB) Data Offset : 144 sectors Super Offset : 8 sectors State : clean Device UUID : 64949ade:b6d618a8:f45a3b07:29ddc35e Internal Bitmap : 8 sectors from superblock Update Time : Fri Sep 18 13:38:41 2009 Checksum : 256ea9d4 - correct Events : 4 Layout : near=2, far=1 Chunk Size : 64K Array Slot : 0 (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) Array State : Uuuuuuuuuuuu After: # mdadm --manage /dev/md0 --fail /dev/sdc mdadm: set /dev/sdc faulty in /dev/md0 # mdadm --manage /dev/md0 --remove /dev/sdc mdadm: hot removed /dev/sdc # mdadm --manage /dev/md0 --add /dev/sdh mdadm: added /dev/sdh [...] # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 sdh[12] sdw[11] sdg[10] sdv[9] sdf[8] sdu[7] sde[6] sdt[5] sdd[4] sds[3] sdr[1] sdb[0] 426970368 blocks super 1.2 64K chunks 2 near-copies [12/12] [UUUUUUUUUUUU] bitmap: 0/204 pages [0KB], 1024KB chunk unused devices: Eeew, /dev/sdh is in slot 12, where is slot 2? And: # mdadm --examine /dev/sdh /dev/sdh: Magic : a92b4efc Version : 1.2 Feature Map : 0x1 Array UUID : 9477b121:204de4c4:a96d58e9:85746699 Name : caronia:testarray2 (local to host caronia) Creation Time : Fri Sep 18 12:59:24 2009 Raid Level : raid10 Raid Devices : 12 Avail Dev Size : 142323568 (67.87 GiB 72.87 GB) Array Size : 853940736 (407.19 GiB 437.22 GB) Used Dev Size : 142323456 (67.87 GiB 72.87 GB) Data Offset : 144 sectors Super Offset : 8 sectors State : clean Device UUID : 31c4a4f5:7aef046d:8981c552:b63165c2 Internal Bitmap : 8 sectors from superblock Update Time : Fri Sep 18 13:56:55 2009 Checksum : b09071e2 - correct Events : 14 Layout : near=2, far=1 Chunk Size : 64K Array Slot : 12 (0, 1, failed, 3, 4, 5, 6, 7, 8, 9, 10, 11, 2) Array State : uuUuuuuuuuuu 1 failed Is it the case that every time I replace a disk I'm going to get a new slot? Doesn't that make the raid "superblock" grow without limit?