[PLUG] MBR in (fake)RAID mirrored disks

[chris mccraw]

On 3/3/08, Michael Rasmussen <michael at jamhome.us> wrote:
>
>  Tim wrote:
>  >> The failing drive the the primary of the pair and it seems the mirrored
>  >> drive doesn't have the MBR written. This seems brain dead.
>  >>
>  >> Is this something that "happens"?
>  >
>  > Yes, this is actually common and in a way, it makes sense.
>  >
>  > You see you are mirroring partitions here, not disks.
>
>
> It seems that all the responses so far assume I implemented RAID with
>  Linux's software.  Instead I used the (MSI motherboard) hardware RAID for
>  the SATA drives.  Which, I thought, mirrored physical devices, not logical
>  segments.
>
>  Not true?

Ugh, that depends entirely on how they want to do it.  I agree that is
a reasonable assumption (as is the one that it would actually cover
the entire physical media as opposed to the last N-X sectors), but
I've learned not to assume anything after my experiences in that
arena.  I was trying to go that route with an asus MB since I figured
I could dual boot and have all the mirroring free and accessible in
win and lin, but the linux drivers never did get around to supporting
the chipset for raid1, so I had software raid on linux and installed
all the windows software on a mirrored samba server instead.  I had to
move that array to another machine when the motherboard and processor
got in a literal flame war, so I was glad I'd gone that way.

If I were the manufacturer and looking for a reason not to support
mirroring the MBR, it'd be that the primary-disk-lacking machine
wouldn't boot without moving the secondary disk to primary considering
that the MBR has drive-order-dependent addresses in it (AFAIK), so the
mirror wouldn't provide for unattended or even
without-opening-the-case-and-cable-pulling failover.


>  Tangent, with good backups I'm wondering if mirroring is worthwhile.
>  It's not like I'm going to buy a now overpriced hard drive to replace the,
>  small by today's standards, one that failed.

You can always replace with whatever the cheapest (same or larger)
drive is...if you switch to software raid.  The other benefit there is
that you are not screwed if the *motherboard* craps out and there's
not a replacement available that understands and is willing to
participate in precisely what the last motherboard did in regards to
mirroring..