GPT Partitions on RAID Disks

["Robinson, Herbie" <Herbie.Robinson@stratus.com>]

Background:

I have been tasked with implementing UEFI boot in our VOS operating system.  We've been using GPT partitions for more than 15 years, but only within our own OS...  We haven't had to interact with any other software before this.  We have a fault tolerant OS; so, all disks are RAID1 (software supported).  We don't expose the GPT partitioning to our user interface:  We have just use it as a wrapper for boot support to keep BIOS from being confused.  The intent was to set it up to boot with either the legacy BIOS or UEFI.  At the time, we only had a legacy BIOS to test with; so, we never finished the UEFI boot.

I've reviewed our current implementation and found a few minor things wrong; so, I have been working on a utility to fix them.  But the might be some more issues.  I have three questions, but relating to RAID 1.


1.       We have historically paired entire disks when we do RAID1, not partitions (we have never supported multiple file system partitions on one disk, because it didn't make sense from a performance standpoint).  I believe the current initialization uses the same DiskGUID in the GPT header for both disks.  I'm assuming that is not going to work properly.  Is that correct?

2.       The spec also seems to say that the UniquePartitionGUID should also be different for RAID 1 pairs.  Is that correct?

3.       We have learned over the years that one doesn't allocate an entire disk for a RAID (because one may have to replace a drive and replacement may not come with exactly the same ending LBA).  We are currently leaving off some space at the end.  When we do that, we are not putting the backup GPT header at the last LBA the devices.  By my reading of the spec, that is a mistake.  I do believe the spec allows me to leave a large gap between the LastUsableLBA in the backup GPT header with the backup table placed anywhere within that gap.  Is that correct?

Thanks in advance for your guidance.
Herbie Robinson
Software Architect
Stratus Technologies | www.stratus.com
5 Mill and Main Place, Suite 500 | Maynard, MA 01754
T: +1-978-461-7531 | E: Herbie.Robinson@stratus.com
[Stratus Technologies]<http://go.stratus.com/US>