Re: RAID, mdadm shift dev point

On 7/17/06, Guillaume <silencer@free-4ever.net> wrote:

Andrea Ganduglia a écrit :
> Hi, I have a problem with unexpected raid behavior. On my machine I have
> configured two raid5 (raid software, mdadm) over 5 disks + 1 spare disk.
>
> md0: sda1 sdb1 sdc1 sdd1 sde1 [UUUUU] (spare: sdf1)
> md1: sda2 sdb2 sdc2 sdd2 sde2 [UUUUU] (spare: sdf2)
>
> Now. I have set fails sdb2 on md1
> ~$ mdadm --fail /dev/md1 /dev/sdb2
>
> md1: sda2 sdc2 sdd2 sde2 [U_UUU] (spare: sdf2)
>
> and hot added sdf2 on same disk array. Array has been rebuild including
> sdf2
> into it:
> ~$ mdadm --add /dev/md1 /dev/sdf2
>
> md1: sda2 sdc2 sdd2 sde2 sdf2 [UUUUU] (spare: none)
>
> Ok, it works well.
>
> Now, for emulate disaster scenario I have halted machine and phisically
> remove
> /dev/sdb. System booted well but /dev point has been shifted by one
> position,
> or, in other words:
>
> sda -now-is-> sda
> sdb -now-is-> sdc
> sdc -now-is-> sdd
> sdd -now-is-> sde
> sdf -now-is-> sde
>
> while sdf is not recognized by the system. Why system reallocate /dev
> point in
> this way? It's a disaster for daily maintenance. Now my /proc/mdstat said:
>
> md0: sda1 sdb1 sdc1 sdd1 sde1 [UUUUU] (spare: none)
> md1: sda2 sdb2 sdc2 sdd2 sde2 [UUUUU] (spare: none)
>
> /dev/sdf do not exist, but it is phisically in my machine.
> while
> /dev/sdb found into raid arrays, but it is phisically on my desk!
>
> Please, help me to understand mdadm logic.
>
>

Hi,

It's not a mdadm logic problem...

That's "/dev" logic problem... Linux assign the first disk as sda, the
second as sdb, and so on

If you remove the first disk, all is shifted by one !!! :-(

Regards
Guillaume