Mirroring

Mirroring

[Mohamed Farouk]

Dear Sir


First i read about your experience in the Unix  Administration, and it 
is ereal great, hoping one day to reach your point.

Second, i have a question concerning the Mirroring technique as i use it 
here, knowing that i am working with RedHat linux 7.2. My question is:


How can i make the slave or the backup disk bootable in case of master 
disk crash?

More exploration:

I have 2 hard disks, one is the master and the other is the slave or the 
backup, or the mirror (whatever), i finished installing them and they 
are working fine (till now !!), but when i make a test to remove anyone 
to see if the other will work properly (as this will be the case in case 
of anyone of them crash), i found that the master one is working fine 
(which contain the boot commands) while the other failed to boot. I 
tried to put a bootable disk but it gives me something related to kernel 
panics.

Your help will be much appreciatted:



-- 
Mohamed Farouk
System Engineer
IT Dept.
MEMScAP
9 St, Ebn Batouta, Beside the Baron, Cairo, Egypt
Tel: 4146860 Ext: 102
Mobile: 0101828653
http://www.memscap.com


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Re: Mirroring

[Gernot A. Weber]

Dear Mr Farouk,

> (which contain the boot commands) while the other failed to boot. I
> tried to put a bootable disk but it gives me something related to kernel
> panics.
>

I assume that you wrote the bootdisk when your master disk was running. So
the LILO searches for the root partition on the master disk. When there is
no master disk it fails to read it. I think it should be enough to write a
new MBR with an alternate lilo.conf, which tells the kernel to boot not
the master disks root partition but the slave root partition. In other
words search for the entry root=. It might say something like
root=/dev/hda1. Change it to the slave disk, eg root=/dev/hdb1 (This
example assumes master / in hda1 and slave / on hdb1). Probably lilo won't
write to MBR and complains about hdb being not first disk. But you can
fake this entry. I can't remember the rigth syntax. But I think a quick
google search should solve this problem.

Best wishes,

   Gernot Weber


-- 
Gernot A. Weber
http://www.tux-web.de

Only wimps use tape backup: _real_ men just upload their important stuff
on ftp, and let the rest of the world mirror it.

                              Linus Torvalds, after a hard drive crash