[gentoo-user] mdadm device removed

[gentoo-user] mdadm device removed

[Kraus Philipp]

Hello,

I'm using a software raid with mdadm (mirror). A few days ago the mdadm removes during the boot process one disk and sets the raid inactive.
The disk contains no errors (smartctl) and nothing is reported in the logs. I reassemble the disk and activate the raid again. Reboot
the system and my disk are in sync and everything works fine.

I'm a little bit confused about it. Does anybody has got an idea, why the array lost a disk?

Thanks

Re: [gentoo-user] mdadm device removed

[Jarry]

On 06-Aug-12 10:50, Kraus Philipp wrote:

> I'm using a software raid with mdadm (mirror). A few days ago the
> mdadm removes during the boot process one disk and sets the raid
> inactive. The disk contains no errors (smartctl) and nothing is
> reported in the logs. I reassemble the disk and activate the raid
> again. Reboot the system and my disk are in sync and everything works
> fine.
>
> I'm a little bit confused about it. Does anybody has got an idea, why
> the array lost a disk?

It may happen quite frequently with common (non-raid) drives
which do not have TLER implemented.

Modern drives have some kind of internal error-recovery
procedure which covers remapping of bad/weak sectors. This
might take quite long time (a few seconds, or even tens
of seconds) and as a result raid-controller (or raid-software)
marks drive as failed because it does not respond in
given time.

Solution is to use "raid-edition" drives, with TLER
(time limited error recovery) implemented. On some drives
this can be activated by using some utility (i.e. WDTLER.EXE).
You can read more about it on the net, i.e.:
http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery
http://en.wikipedia.org/wiki/RAID#Problems_with_RAID

Jarry
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