Re: EDD disksigs for disks other than 0x80

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On Fri, Jun 25, 2004 at 10:53:45AM -0400, Jeremy Katz wrote:
> On Thu, 2004-06-24 at 15:40 -0500, Matt Domsch wrote:
> > Patch below against 2.6.7-bk(current) gives mbr_signature for first
> > six BIOS disks.
> 
> Seems to work, at least for two (all that I have handy on a test machine
> right now).

Cool.  I realized last night that we sell servers with 12 disks in the
main 7U chassis, not counting any external storage.  So I'm reworking
to code to allow storing MBR signatures for up to 16 disks.  There's
no real BIOS limitation at 16 or lower, but in practice it's rare to
see more BIOS disks than this, and it takes 4 bytes of the real mode
boot_params block per signature we might want to store, so I don't want
it to get out of hand.

> Unfortunately, the mbr_signature on both of those disks
> (and the sig on the first from before rebooting into the newer kernel)
> is 0x00000000.  So I guess these don't have any guarantee of uniqueness?

Right.  The uniqueness guarantee has to come from whatever writes the
signatures to the disk in the first place.  There should have been in
Rez's code a little chunk which, when it detects non-uniqness among
the disks visible to Linux, it writes unique signatures to those
disks, then reboots, such that when we restart, all the disks have
unique signatures.

fdisk and parted presently always write zeros to the 4-byte signature
field at offset 0x1b8 in the MBR.  Dell's factory install tools will
write a unique signature to each BIOS-visible disk, so we're good
there.  Anaconda will need similar code.

Thanks,
Matt

-- 
Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com

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