Re: only 4 spares and no access to my data

[Nix <nix@esperi.org.uk>]

On 18 Jul 2006, Neil Brown moaned:
> The superblock locations for sda and sda1 can only be 'one and the
> same' if sda1 is at an offset in sda which is a multiple of 64K, and
> if sda1 ends near the end of sda.  This certainly can happen, but it
> is by no means certain.
> 
> For this reason, version-1 superblocks record the offset of the
> superblock in the device so that if a superblock is written to sda1
> and then read from sda, it will look wrong (wrong offset) and so will
> be ignored (no valid superblock here).

One case where this can happen is Sun slices (and I think BSD disklabels
too), where /dev/sda and /dev/sda1 start at the *same place*.

(This causes amusing problems with LVM vgscan unless the raw devices
are excluded, too.)

-- 
`We're sysadmins. We deal with the inconceivable so often I can clearly 
 see the need to define levels of inconceivability.' --- Rik Steenwinkel