Mailinglist Archive: opensuse (1196 mails)

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Re: [opensuse] Does openSuSE Ever run fsck on disks in dmraid array with nvidia controller?
  • From: Per Jessen <per@xxxxxxxxxxxx>
  • Date: Thu, 28 Jan 2010 09:12:51 +0100
  • Message-id: <hjrgu4$rqd$1@xxxxxxxxxxxxxxxx>
David C. Rankin wrote:

The question is still pending though. How are (whatever these errors
are) handled by suse when a disk is part of an dmraid array? You
cannot fsck the disk when it is part of the array because fsck exits
and throws the error that the disk is 'under the exclusive control of
another process' and refuses to test the disk.

You do not have a need to fsck any individual disk that is part of an
array. fsck checks the filesystem, so you run fsck on the array device
that holds your file system. That's it. Any errors with an individual
drive will be reported by the array controller (whether software or
hardware).

What I want to know is: "Is there any individual disk level error
correction performed on disks in dmraid arrays, or is it as it looks
-- no fsck error correction is ever performed on individual disks in a
dmraid array?"

The latter.

The ultimate question is should I ditch dmraid entirely and go with
mdraid? dmraid has been absolutely bullet-proof as has been my mdraid
installs. But, if mdraid can handle single disk error correction
within an array where dmraid can't, that would be enough justification
for me to dump dmraid in favor of mdraid.

AFAICT, mdraid does not "handle" a drive error any better or any worse.
It would report it and run the array in degraded mode. What dmraid
does will presumably depend on what your hardware controller does. I.e.
when your RAID chipset decides the mirror is bad, how does it inform
you?

dmraid and mdraid are incredibly similar in the flexibility they offer
as a raid solution. In either case you have mirrored copies, where
upon failure, or just for kicks, you can rip one disk out of the array
and boot and run on a single disk, or put it in another box without
any concern about raid incompatibility. Both just use normal
partitions and disks, the only primary difference is in how they are
joined, either through a bios function or through a software function.

I could be way wrong, but my understanding is that dmraid is an
interface to various hardware/on-board RAID controllers, whereas
mdraid actively does the mirroring.

I have liked dmraid because I can easily mirror /, /boot, /home and
swap on each disk so that in the event of disk failure, the most work
one disk can ever need to act as a standalone is to reinstall grub in
the mbr if the boot loader code just happened to be other disk. (small
potatoes)

FYI, mdraid will do that too, no big deal. Isn't that the whole point? I
think the primary difference between the two is that mdraid takes up
CPU cycles doing the mirroring, dmraid does not.


/Per

--
Per Jessen, Zürich (-1.9°C)

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