[CALUG] Hardware Mirroring

David A. Cafaro dac at cafaro.net
Sat Oct 15 08:57:06 CDT 2005

If you are doing true hardware mirroring, your OS should never see the
second drive.  The hardware raid controller handles the individual drive
management and then presents a virtual single disk to your Operating
system.  In this situation you only need to install grub to the disk
that the hardware raid is presenting to it (one install), since the
hardware will take care of making two copies one on each disk.  If there
is a drive failure then the hardware raid controller will take care of
autoswapping to the other drive.

The above is all true for real hardware raid.  I'm not familiar with the
megaraid so I'm not 100% it's true hardware raid.  There are hardware
raids out there that are really software raids with some hardware
support (like the Nvidia raid controllers built into their
motherboards).  These require installing drivers into the OS to be able
to work with the raid hardware.  If you had to install special drivers
or load special drivers (besides basic SCSI or IDE/SATA drivers) then
the stuff above about hardware raid may not be true.

One clue on if it is real hardware raid vs software raid, if you
configure the raid through a bios like screen then it's probably real
hardware raid.  If you have to install software in your OS to configure
the raid then it's probably a hybrid soft/hardware raid.


On Sat, 2005-10-15 at 08:25 -0400, Rajiv Gunja wrote:
> Does anyone in the group used hardware mirroring?, if so, have you installed
> grub on both boot disks ?
> Explanation of my Question:
> I recently obtained a Dell server which lets me do hardware mirroring on its
> internal drive using megaraid. I intend to install either RHEL 4 or SLES 9.
> For redundency, I mirrored the boot disks via hardware mirroring. Now I can
> install grub on the first disk, but not on the second disk. The basic
> thought being that if the first disk goes bad, the second disk should be
> bootable. Every time I try to install grub on it, it fails -> core dump. So
> the only way I can boot through the second disk is via a floppy drive, which
> is kind of annoying, as i have to make sure that the floppy disk is not
> currupted.
> I have looked at RH website and there is no solution for hardware mirror,
> however they have solution for the same for a software mirroring.
> Anyone, any clues?
> -GGR
> ---
> Rajiv G Gunja
> System Analyst / Engg
> SUN / AIX / HPUX / Linux Admin
> IM: AOL / Yahoo / MSN : ggvrsn
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David A. Cafaro
Tech to Admin: "I thought I did plug that in..."

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