On Tue, Jun 26, 2012 at 01:37:11PM -0400, John Baldwin wrote: > > 4. The gptboot now searches the backup GPT header in the previous sectors, > > when it finds the "GEOM::" signature in the last sector. PMBR code also > > tries to do the same: > > common/gpt.c > > i386/pmbr/pmbr.s > > GPT really wants the backup header at the last LBA. I know you can set it, > but I've interpreted that as a way to see if the primary header is correct or > not. [...] My interpretation is different: The way to verify if the header is valid is to check its checksum, not to check if the backup header location in the primary header points at the last LBA. Of course if primary header's checksum is incorrect it is hard to trust that the backup header location is correct. And we need the backup header when the primary header is invalid... > [...] It seems to me that GPT tables created in this fashion (inside a GEOM > provider) will not work properly with partition editors for other OS's. I'm > hesitant to encourage the use of this as I do think putting GPT inside of a > gmirror violates the GPT spec. I don't think so. Most common case is to configure partitions on top of a mirror. Mirroring partitions is less common. Mostly because of hardware RAIDs being popular. You don't expect hardware RAID vendor to mirror partitions. Partition editors for other OS's won't work, but only because they don't support gmirror. If they wouldn't recognize and support some hardware (or pseudo-hardware) RAIDs there will be the same problem. In other words, IMHO, our problem is that FreeBSD's boot code doesn't recognize/support gmirror's metadata. What Andrey is proposing is to recognize the metadata and act accordingly - in case of a gmirror we simply need to skip it. In the future we will have the same problem with graid - until we add support for it to the boot code, we won't be able to boot from it. -- Pawel Jakub Dawidek http://www.wheelsystems.com FreeBSD committer http://www.FreeBSD.org Am I Evil? Yes, I Am! http://tupytaj.pl
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