[ydl-gen] Software RAID - making the spare bootable

[Derick Centeno]

Question:
Correct me if I missed something, but wasn't the third "spare" intended 
to be an exact mirror so that it could replace either the first or 
second drive?

For the "spare" to be a replacement for either the first or the second 
drive it also would have matched the exact partition structure of the 
first two.  In this particular sense the "spare" is really no "spare" at 
all, but a sort of emergency last ditch fail-safe in the event that 
either the first or second drive failed.  This also means that the for 
the RAID 1 system to function with a fail-safe option/strategy the third 
drive had to be prepared properly so that it could potentially replace 
any one of the other two at any time.

Zeroing the RAID superblocks and attempting to make the Apple partition 
bootable via ybin may have been mistakes; however the strategy to dd the 
second (or first) drive onto the "spare" appears reasonable.

Is it possible to reformat/restructure all three disks, using YDL, so 
that function is restored?

On 12/13/10 2:37 PM, Matt Brock wrote:
> Hi there.
>
> (I posted this onto the YDL forums earlier today, so apologies to 
> anyone who's seen it twice.)
>
> I've been using YDL on Xserve G5s for a couple of years now and it 
> does a great job. Recently I decided to rebuild one with software RAID 
> to get disk redundancy. I did all of this through the installer. The 
> server has three disks, so I set them up as RAID 1 with a spare.
>
> This has all gone very successfully apart from one detail. The two 
> disks in the RAID set are bootable, i.e. I can remove either of those 
> disks and the machine will still boot as normal. That's fine so far. 
> Then I permanently removed the first disk and brought the spare third 
> disk into the RAID set instead. Once the RAID set is then fully 
> rebuilt I can boot off the original second disk, but the third disk 
> which was previously the spare disk is not bootable. It gets to the 
> first yaboot stage, and then the blue icon which represents OpenBoot 
> failing to find a boot disk appears superimposed over the yaboot 
> screen. That process just loops over and over again and never boots.
>
> I've tried using ybin to make the Apple boot partition bootable with 
> the correct yaboot config, but that didn't help. I've tried dd-ing the 
> entire second disk onto the third disk then zeroing the RAID 
> superblocks, and that didn't work. I've tried resetting the NVRAM and 
> that made no difference. I'm sure it's not a hardware problem with the 
> disk because I've tried this twice now with the disks in different 
> slots each time, and it's always the spare disk which has the boot 
> problem even though that's a different physical disk each time.
>
> I hope there's someone out there who can help because I'm tearing my 
> hair out over this. I can't see what else would be needed to make the 
> third disk bootable... yet there must be something! Without getting 
> this working the full redundancy I'd hoped for can't be achieved, 
> which would be extremely frustrating.
>
> Cheers,
>
> Matt.
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