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I was told that the SCSI mode page commands that provide serial numbers are an optional feature. Is this true?

Grub2 most definitely fails to function on disks that do not provide serial numbers. See LP: #604335 for details. The key issue is that while the /usr/bin/grub-install script does not look at /dev/disk/by-id/* files, the code that running "sudo dpkg-reconfigure grub-pc" executes looks for only disks that provide serial numbers by using the contents of /dev/disk/by-id/* as the source of information.

One of the critical aspects of this is that VMware Fusion /dev/sda emulated disks fail to provide serial numbers (comment #44 in LP: #604335 above) so they fail with grub-pc.

How many non-virtual disks do not implement serial numbers and therefore cannot be used with grub2 correctly?

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I just noticed that in Ubuntu 11.10 Oneiric the grub-pc version 1.99-12ubuntu5 running inside VMware Fusion 4.1.1 (536016) most definitely does not have SCSI serial numbers for /dev/sda etc. virtual drives yet has working "dpkg-reconfigure grub-pc".

Look in /dev/disk/by-id/ and none of the symlinks are to sda, that confirms there are no SCSI serial numbers.

Something was likely updated in the script(s) that the grub-pc package contains to be able to cope with having no /dev/disk/by-id/ symlinks. I will go take a look at what it is that was done. I also have to check to see what is up with 10.04 LTS if anything since this affects KVM guests with virtio /dev/vda disks too. Later versions of Ubuntu past 10.04 support using <serial>foo</serial> in libvirt xml and that works to create /dev/disk/by-id/ symlinks provided you have a new enough udev to create /sys/block/vda/serial

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