growing md2, do I need three reboots?

[Janek Kozicki <janek_listy@wp.pl>]

Hello,

my /dev/md2 uses superblock 1.0, which is stored at the end of
device. Therefore I suppose that this approach of growing it isn't
going to work:

  #Alter the partition tables, to make /dev/sd[abc]2 have new size:
  fdisk /dev/sda
  fdisk /dev/sdb
  fdisk /dev/sdc

  #reboot (make kernel read new partition table)

  #then, grow the raid1 /dev/md1
  mdadm --grow /dev/md2 --size=max

  #and finaly, grow the ext2 (or ext3) fs on /dev/md1
  resize2fs /dev/md1

Because in this way, after rebooting, /dev/md2 won't be found - the
superblock won't be in the correct place.

So, I would need to remove each of them from the array, resize
partition, then add it back. Thus needing three reboots, since I can
remove only one device at a time (the same HDDs have also partitions
belonging to root raid1 array), which must be always up & running.

I can afford reboots, no problem here, but isn't there some simpler way?


below is my raid layout, I need to grow md2 by few spare gigabytes
left at the end of /dev/sd[abc].

kernel 2.6.29 (impossible to upgrade at the moment).

Personalities : [raid0] [raid1] [raid10] 
md2 : active raid10 sda2[0] sdc2[2] sdb2[1]
      185381376 blocks super 1.0 512K chunks 2 far-copies [3/3] [UUU]
      bitmap: 1/6 pages [4KB], 16384KB chunk

md1 : active raid1 sdc1[2](W) sdb1[3](W)
      9767416 blocks super 1.0 [2/2] [UU]
      bitmap: 1/150 pages [4KB], 32KB chunk

md0 : active raid1 sde1[0] sdd1[2] sda1[1]
      9767424 blocks [3/3] [UUU]
      bitmap: 1/150 pages [4KB], 32KB chunk

unused devices: <none>
atak:/home/janek# mdadm -D /dev/md2
/dev/md2:
        Version : 1.0
  Creation Time : Thu Sep  2 11:47:39 2010
     Raid Level : raid10
     Array Size : 185381376 (176.79 GiB 189.83 GB)
  Used Dev Size : 123587584 (117.86 GiB 126.55 GB)
   Raid Devices : 3
  Total Devices : 3
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Thu Dec  2 16:41:02 2010
          State : active
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : far=2
     Chunk Size : 512K

           Name : atak:2  (local to host atak)
           UUID : f2a75dbe:5ac91a1f:c09da3c0:f6f69c9c
         Events : 28

    Number   Major   Minor   RaidDevice State
       0       8        2        0      active sync   /dev/sda2
       1       8       18        1      active sync   /dev/sdb2
       2       8       34        2      active sync   /dev/sdc2

best regards
-- 
Janek Kozicki                               http://janek.kozicki.pl/  |