Mirror disk - emergency procedure - how ?

Mirror disk - emergency procedure - how ?

Post by Holger Burd » Wed, 17 Nov 1999 04:00:00



Hi;

I am looking for a simple emergency procedure for one of our Linux
Servers.
My idea is to mirror the whole Disk so i can simply switch to the
mirror disk in case of a device failure. The procedure has to be as
simple and fast
as possible (no case opening,Jumper changing etc)!

I have 3 disks

sda: / /usr /opt
sdb: mirror
sdc: not really important ...

I case of a failure i would perhaps replace the disk if one is available
at that time ...
or just boot from sdb. _Worst_case_ is no news disk is available or no
time to dd the stuff to the new disk !

Procedure :

a) change /etc/fstab (with bootable INSTALL CD)
b) make sdb the first bootable disk (via Adapetec BIOS)
 CTRL D and go

I verified that dd works - did a fsck - also ok. The only think i am not
sure
about is how lilo looks at disks (didn't test this). I have written lilo
to the MBR
of sda so this is also on sdb. This would work if lilo operates with an
idea
where to boot from like: this.disk:this.slice and not
dev(targetID).slice

If the 2nd is true what can i do ??? Is there a way to run lilo from the

RH6 bootable CDROM or better before and how does the cmdline should look
????

Thanks in advance

hb

 
 
 

Mirror disk - emergency procedure - how ?

Post by AJ » Wed, 17 Nov 1999 04:00:00


No need to post so much -- we'll get to you as soon as we can =8^)

Quote:> I am looking for a simple emergency procedure for one of our Linux
> Servers.
> My idea is to mirror the whole Disk so i can simply switch to the
> mirror disk in case of a device failure. The procedure has to be as
> simple and fast
> as possible (no case opening,Jumper changing etc)!

If you have a device failure, unless you have a RAID tower, you'll probably
have to open the case. My suggestion? Don't put any screws in the thing and
pop it open (takes all of two seconds). Besides that, have you looked into
software RAID? (check out the how-to) If that doesn't agree with you, then
you can go

Quote:> I have 3 disks

> sda: / /usr /opt
> sdb: mirror
> sdc: not really important ...

Sounds good enough...

Quote:> I case of a failure i would perhaps replace the disk if one is available
> at that time ...
> or just boot from sdb. _Worst_case_ is no news disk is available or no
> time to dd the stuff to the new disk !

You are going to need a boot floppy -- my suggestion is create one that sits
inside the floppy drive, or just use a disk like tom's root/boot linux
(http://www.toms.net).

Quote:> Procedure :

> a) change /etc/fstab (with bootable INSTALL CD)
> b) make sdb the first bootable disk (via Adapetec BIOS)
>  CTRL D and go

You won't need to -- when sda fails, then sdb becomes sda...

Quote:> I verified that dd works - did a fsck - also ok. The only think i am not
> sure about is how lilo looks at disks (didn't test this). I have written
lilo
> to the MBR
> of sda so this is also on sdb. This would work if lilo operates with an
> idea where to boot from like: this.disk:this.slice and not
> dev(targetID).slice

Like I said, you'll wanna install a bootfloppy for your system. Use Tom's
Root/Boot in case that doesn't work (my suggestion is to always have two
copies of toms'root/boot linux floppies available at all times). The boot
floppy should be pointing to /dev/sda, and since it crashed, your 2nd disk
becomes /dev/sda instead of /dev/sdb as it was before. Now -- You WILL have
problems with your third drive, so you'll wanna edit the fstab once you get
it booted to show that your third drive is no /dev/sdb...

I know this gets confusing as hell, so you'll have to go by trial and error.
The other how-to to read would be Hard Disk Upgrade mini-HOWTO. That one
gives off a lot of info as well...

Take care and good luck.

AJ

 
 
 

Mirror disk - emergency procedure - how ?

Post by AJ » Wed, 17 Nov 1999 04:00:00


Almost forgot, one other very important thing that you can not forget:

Do Daily Backups!