Re: raidframe performance question

[David Laight <david%l8s.co.uk@localhost>]

On Wed, Jun 15, 2011 at 06:37:58PM +0200, Joerg Sonnenberger wrote:
> On Wed, Jun 15, 2011 at 11:23:48AM -0500, Dave Burgess wrote:
> > If anyone has any idea how to get the RAID-5 array to boot after the
> > "raidctl -A root" and the appropriate disklabel and installboot
> > directives, I'd love to hear them.
> 
> The boot loader only supports RAID1 by effectively ignoring it.

Worse than that really!
The code that loads /boot has another look 64 sectors down the disk if
it fails to find it (in the filesystem) at the expected offset
(this skips the RF header).

Booting from RAID-5 would require that the low level boot code understood the
RF parameters. Particularly nasty for raid-5 if one of the disks has died.

Plausibly the code in /boot could understand the RF header - allowing the
kernel (and modules) be read from the raid, but everything earlier
isn't likely to be changed.

Unless, of course, the system bios is able to do it - and the disk number
used requests the raid accesses.

I did once jave a plan to let sysinst install to a raid-1 single disk - to
which a mirrored copy could be later added.
In theory sysinst could install to a real raid-1 without having to rebuild
the raid at all - since the contents of unwritted sectors are 'don't care'.
(OTOH that might be rather connfusing much later on!)

        David

-- 
David Laight: david%l8s.co.uk@localhost