[clug] mirroring scsi drive

Eyal Lebedinsky eyal at eyal.emu.id.au
Sat Sep 6 16:34:36 EST 2003

"nicolas.cherbuin" wrote:
> Hi,
> I have an old IBM server at home with two 9.1GB scsi drives. On one I have
> installed RH 9, on the other there is an old version (RH 7.2).
> What I am trying to do is mirroring the first one on the second one. My
> problem is that when the two drives are inserted the computer boots on RH 7.2.
> As the first drive is scsi 7 device, it occurred to me that maybe I needed
> to change the jumper so that the first drive is "seen" first but after
> taking the drive out of its tray I could not see any jumper switches...
> (plus I would not know how to change the other drive's jumpers as nothing
> is written about it on the drive itself)

It is better to boot from CD, then you can see the other disks just
I will also make the 'dd' that you mention later more reliable as there
will not be any open files on the source. There are rescue floppies that
can do this too if you cannot boot from a CD.

> I have also  tried to boot from the first drive and then insert the second
> drive but I cannot find the second drive (doing something like fdisk
> /dev/sdb, but the second drive is probably also called sda since it has its
> own version of RH on it).

No, the two disks will have unique names when each system is booted. You
can look at the boot messages to see what each disk is called. It is
critical that you absolutely know which one is the "good source" and
which is the target that will be overwritten.

> So, my question: how do I format the second drive and make it visible to
> the system. And secondly while I am at it, I was going to use:
> dd if=/dev/sda of=/dev/sdb bs=1M   (I know nothing about dd but that's what
> I have found in FAQs)
> Is this a good way of doing it, and do I need first to create identical
> partitions on drive 2 as on drive 1, and if yes, how do I do that?

This is fine, it will copy the partition table too (I assume the two
are identical). Best dome when the source is unmounted, but make sure
you /dev/sda is really the source you want to copy (mount, inspect it,

Be careful, you can blow your data away easily when working at this low
level. Naturally, you should take good backups before starting this

Good luck.

Eyal Lebedinsky (eyal at eyal.emu.id.au) <http://samba.org/eyal/>

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