On Tue, May 28, 2002 at 09:20:39PM +0200, Danilo Godec wrote:
> On Tue, 28 May 2002, James Fillman wrote:
...
> I think this shouldn't work at all - have you rebooted the machine yet?
>
> It's not quite clear how the mirrors reconstruct if one of the disks
> (partitions) already has a filesystem on it, but I'm almost sure it's not
> ment to reconstruct it properly...
Either it reconstructs it "right" or it does it "wrong". It seems in his case
it did it right. Lucky him.
Hoever, the persistent superblocks will overwrite the last few KB of his
*filesystem* on each partition. So things *may* seem to work, but the
system will fail horribly later. After an fsck the RAID suprblocks will
be damaged. After another mkraid the filesystem will be damaged again.
>
> AFAIK making a filesystem on a Linux SW RAID array is somewhat different
> from making it on a 'normal' disk, so while you may end up with a
> filesystem, it will probably be full of errors.
Yep.
>
> How does your raidtab look like?
>
> The 'right' way of doing this is:
>
> - create a 'degraded' mirror with sda* partitions marked as 'failed'
> - copy all the data from sda* partitions to the appropriate mirrors
> (/dev/md*)
> - modify /etc/fstab on the mirrored filesystem to use the mirrors
> - reboot, use filesystems on the mirror (root=/dev/md?)
> - hot add sda* partitions to approprate mirrors (using raidhotadd or
> mdadm)
> - wait for the reconstruction to finish
> - make sure that both disks have the boot loader installed in MBR, so they
> can both be used for booting
Yep.
>
> This should be it. Unfortunately, this procedure is not that easy to
> script.
I suppose that if the installation kernel (the one booted during the installation
process) could be made to support RAID (with autodetection), you could just create
the RAID arrays prior to installation, and then simply install on those arrays.
But that may require some hacking of the SuSE install disk...
>
> > the mkraid command warns me that it will delete all the data on the partitions
> > when creating the mirrors, but it doesn't.
>
> I guess it doesn't delete the data, it destroys it... :)
Just a small amount of it. It "almost doesn't totally f*ck up the system" ;)
>
> > What sort of implications am I looking at with this? Will it be unstable?
>
> I am no super-expert or guru, but I'd say YES. Try booting the system with
> a rescue disk and run e2fsck on your mirrored filesystems. If this goes
> through OK... Well, then I might be wrong and it's OK to do this with new
> kernel/raidtools...
I'd say you're right about the failures.
--
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