Thank you all, it seems to have finished - I'm rebooting.
Just curious why is the State of md3 "active", while the others are "clean"?
# cat /proc/mdstat Personalities : [linear] [raid0] [raid1] md0 : active raid1 sda1[0] sdb1[1] 1023936 blocks [2/2] [UU]
md1 : active raid1 sda3[0] sdb3[1] 20479936 blocks [2/2] [UU] [=================>...] resync = 86.6% (17746816/20479936) finish=0.3min speed=131514K/sec
md2 : active raid1 sda5[0] sdb5[1] 277728192 blocks [2/2] [UU]
md3 : active raid1 sda6[0] sdb6[1] 185151360 blocks [2/2] [UU]
unused devices: <none>
..........Then after some wait:.......
# cat /proc/mdstat Personalities : [linear] [raid0] [raid1] md0 : active raid1 sda1[0] sdb1[1] 1023936 blocks [2/2] [UU]
md1 : active raid1 sda3[0] sdb3[1] 20479936 blocks [2/2] [UU]
md2 : active raid1 sda5[0] sdb5[1] 277728192 blocks [2/2] [UU]
md3 : active raid1 sda6[0] sdb6[1] 185151360 blocks [2/2] [UU]
unused devices: <none>
# mdadm -D /dev/md3 /dev/md3: Version : 00.90 Creation Time : Sat Mar 19 22:53:25 2011 Raid Level : raid1 Array Size : 185151360 (176.57 GiB 189.59 GB) Used Dev Size : 185151360 (176.57 GiB 189.59 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 3 Persistence : Superblock is persistent
Update Time : Thu Apr 28 21:31:12 2011 State : active Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0
UUID : 1b3668a3:4b6c5593:3d186b3c:53958f34 Events : 0.39
Number Major Minor RaidDevice State 0 8 6 0 active sync /dev/sda6 1 8 22 1 active sync /dev/sdb6
# mdadm -D /dev/md1 /dev/md1: Version : 00.90 Creation Time : Sat Mar 19 22:52:20 2011 Raid Level : raid1 Array Size : 20479936 (19.53 GiB 20.97 GB) Used Dev Size : 20479936 (19.53 GiB 20.97 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 1 Persistence : Superblock is persistent
Update Time : Thu Apr 28 21:33:56 2011 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0
UUID : 8812725b:ea156bc6:3d186b3c:53958f34 Events : 0.48
Number Major Minor RaidDevice State 0 8 3 0 active sync /dev/sda3 1 8 19 1 active sync /dev/sdb3
# mdadm -D /dev/md0 /dev/md0: Version : 00.90 Creation Time : Sat Mar 19 22:52:12 2011 Raid Level : raid1 Array Size : 1023936 (1000.11 MiB 1048.51 MB) Used Dev Size : 1023936 (1000.11 MiB 1048.51 MB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent
Update Time : Thu Apr 28 21:06:24 2011 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0
UUID : 87db17c2:d806a38c:3d186b3c:53958f34 Events : 0.14
Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 1 8 17 1 active sync /dev/sdb1
# mdadm -D /dev/md2 /dev/md2: Version : 00.90 Creation Time : Sat Mar 19 22:52:32 2011 Raid Level : raid1 Array Size : 277728192 (264.86 GiB 284.39 GB) Used Dev Size : 277728192 (264.86 GiB 284.39 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 2 Persistence : Superblock is persistent
Update Time : Thu Apr 28 21:17:54 2011 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0
UUID : 2db0174b:e45768d5:3d186b3c:53958f34 Events : 0.14
Number Major Minor RaidDevice State 0 8 5 0 active sync /dev/sda5 1 8 21 1 active sync /dev/sdb5