Hello,
I am trying to understand and practice RAID1 functionality: for that
purpose I created two partitions on the same device (yes,
I know that it is recommended that the partitions are
better to be on differrent devices when using RAID1, but this
is for testing purposes only ).
My device is a 64 K USB Disk On Key. (on /dev/sdb)
Than I ran:
dd if=/dev/zero of=/dev/sdb bs=1M count=64
then I created 2 primary partitions for RAID1 with fdisk:
/dev/sdb1 and /dev/sdb2.
fdisk -l /dev/sdb shows :
Disk /dev/sdb: 65 MB, 65470464 bytes
3 heads, 42 sectors/track, 1014 cylinders
Units = cylinders of 126 * 512 = 64512 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 256 16107 fd Linux raid autodetect
/dev/sdb2 257 513 16191 fd Linux raid autodetect
Both Partitions are of type Linux raid autodetect ("fd").
The partitions are equal in size (256 cylinders each)
Then I created a RAID1 by running:
mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/sdb1 /dev/sdb2
I got : mdadm: array /dev/md0 started
cat /proc/mdstat shows:
Personalities : [raid1]
md0 : active raid1 sdb2[1] sdb1[0]
16000 blocks [2/2] [UU]
[==>..................] resync = 12.5% (2112/16000)
finish=0.7min speed=301K/sec
unused devices: <none>
I created ext3 fs on /dev/md0 and /dev/sdb1 and /dev/sdb2.
I found out that I can mount /dev/md0 , but I cannot
mount /dev/sdb1 or /dev/sdb2.
when I try : mount /dev/sdb1 /mnt/sdb1/
I get mount: /dev/sdb1 already mounted or /mnt/sdb1/ busy
I found out that if I stop the RAID (and unmount /dev/md0),
I am able to mount /dev/sdb1 and /dev/sdb2. I also found
out that a file I created (on the path where /mnt/md0
was mounted) was mirrored to /dev/sdb1 and /dev/sdb2, as it should
in RAID1.
The problem is that I cannot run again the RAID
after stopping it.
I stopped it by:
mdadm --stop /dev/md0
cat /proc/mdstat
Personalities : [raid1]
unused devices: <none>
I tried to run it again by:
mdadm --run /dev/md0
mdadm: failed to run array /dev/md0: Invalid argument
Why is it so ?
what is the way to stop and than run again a RAID ?
Am I doing something wrong ? any idea?
Regards,
Ian
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