On Thu, 28 Jun 2012 08:33:17 -0700 Marcel Moolenaar <marcel@xcll...>
> My advise is to leave disk mirroring to H/W or firmware solutions and
> use FreeBSD mirroring for FreeBSD partitions only. If you want to
> mirror the whole disk, don't partition the disk with non-FreeBSD
> partitioning schemes and partition only with FreeBSD-specific schemes
> or put a FreeBSD file system on the whole disk. In other words: make
> the whole disk private to FreeBSD.
If I gmirror the entire disk, I already expressed my interest to make
the whole disk private to FreeBSD, haven't I? Or are you suggesting to
convince all BIOS vendors to include the ability to boot from some kind
of FreeBSD private partitioning scheme (not MBR as it is not
suitable, not GPT as you are not OK to use it on a gmirror)?
> Whether or not people agree with this is besides the point. All I'm
> saying is that unique disk identifiers such as the
> "UniqueMBRSignature" (a 4 byte ID written at offset 440 in the MBR)
> or the "DiskGUID" (an UUID written to offset 56 in the GPT header)
> cannot, in general, be mirrored across disks if OSes can see the
> mirrored disks as independent entities. One violates the spec on
> grounds of making the *unique* disk identifier non-unique by
> presenting OSes with multiple disks that have identical IDs.
What about multipathing? In case the disk is attached via two paths but
multipath is not enabled, the OS sees the same disk (and the same
identical unique disk identifier) multiple times. Is this a violation
of the spec too?