On Jun 28, 2012, at 3:10 AM, Stefan Esser wrote: > > All of the above is ugly, U'm afraid :(
Indeed. The only sane way is to put the metadata in a partition of its own. Every compliant OS will respect that and consequently will not scribble over the data unintentionally. Any other scheme that puts valuable data in some undocumented or unregistered location is violating the GPT spec right away and is susceptible to being clobbered unintentionally. If the metadata is in its own partition, one can document the metadata layout and providing a reference implementation. That way one increases the chance that someone, somewhere may port support for it to some other OS. Lacking widespread support for the mirroring scheme, I think that the notion that one can safely and reliably mirror entire disks (read: mirror data not owned or controlled by FreeBSD) is a very questionable one -- all one has to do is boot some other OS and start modifying one of its partitions and you've failed to achieve the objective. 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. 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. -- Marcel Moolenaar mar...@xcllnt.net _______________________________________________ email@example.com mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"