Re: Mdadm -- Restoring an array

[Hal Vaughan <hal@thresholddigital.com>]

On Tuesday 17 October 2006 17:34, michael wrote:
> > In the future, I'll build my own .conf files just to be sure.  In
> > the long run, I'm just going to find a RAID controller that does
> > hardware RAID5, preferably one that's hot swappable, and just
> > rebuild the RAID on that.
> >
> > > I also like to run / from a raid array. /boot is a mirror,
> > > and so any faulty drive will keep the system bootable.
> >
> > Are you saying / includes a /boot partition and you still have a
> > separate /boot partition?  That's a cool way to set it up.  I've
> > got some extra drives and might be able to work out something
> > similar. Without the /boot mirror, will Linux be able to boot the
> > RAID directly?  I didn't think that was possible.
>
> Hope you get your array back, I'm not sure what else to try.
> No backup?

I can rebuild what is not dispensable, but 1) It'd be easier to restore, 
and 2) I thought I knew how to restore (guess I was wrong), so I'd like 
to figure that out so I can do it in the future, if needed.

I'm sure it's just a matter of finding out what I need to do in the 
config file.  What's puzzling is when I type:

mdadm --examine --scan /dev/hde /dev/hdf /dev/hdg /dev/hdh

I get:

ARRAY /dev/md0 level=raid5 num-devices=3 
UUID=d6fd4af2:5e5d0da2:9dec7c5f:ad60c25d
   devices=/dev/hdf

I thought /dev/hde was the first drive, but it's possible for some 
reason I used /dev/hdf.  That means I'm not sure which of the four was 
the spare.  I don't see why it only recognized hdf and didn't include 
the other two "in use" drives as well (I can understand it leaving out 
the spare).

I tried to find a mailing list for mdadm or a FAQ and found the closest 
it has to a mailing list is the Linux Kernel list.

> Yes, you can create a seperate partition for /boot. It must be a
> single partition, drive, or best of all, raid 1 array. Nothing else.
> Without /boot seperate, your kernel can't load.
> / can be a raid 5, or raid 0 or whatever.
> Because your /boot isn't a fancy array, the kernel will load, tehn
> load up mdadm to create your root raid array and then mount /.

Cool.  I didn't realize that.  I have some small 2GB drives that I could 
easily use as a RAID 1 for the boot.  (It's a shame you can't still get 
small drives like that for cheap!)

Hal