Either I've grossly understood how Linux RAID and/or the mdadmin
command works, or this is horribly wrong:
Device Boot Start End Blocks Id System
/dev/sdb1 1 33 265041 fd Linux raid autodetect
Device Boot Start End Blocks Id System
/dev/sdc1 1 33 265041 fd Linux raid autodetect
$ mdadm --create /dev/md0 --verbose --level=mirror --raid-devices=2 /dev/sdb1 /dev/sdc1
[wait for mirror to sync]
$ cat /proc/mdstat
Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 sdc1[1] sdb1[0]
264960 blocks [2/2] [UU]
unused devices: <none>
Okay, now simulate (without physically changing any disks) a failure,
and then a replacement:
$ mdadm /dev/md0 -f /dev/sdc1 -r /dev/sdc1
mdadm: set /dev/sdc1 faulty in /dev/md0
mdadm: hot removed /dev/sdc1
$ mdadm --zero-superblock /dev/sdc1
$ mdadm /dev/md0 -a /dev/sdc1
mdadm: hot added /dev/sdc1
But the mirror doesn't sync (!):
$ cat /proc/mdstat
Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 sdc1[2] sdb1[0]
264960 blocks [2/1] [U_]
unused devices: <none>
Have I completely misunderstood how Linux software RAID is supposed to
work? (I certainly hope so, because otherwise, it can't even perform
the simplest of recovery operations: replacing a failed mirror
component and re-syncing.)
Thanks for any comments...
--
James Ralston, Information Technology
Software Engineering Institute
Carnegie Mellon University, Pittsburgh, PA, USA
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