Re: 63 sectors

[Gerd Hoffmann <kraxel@redhat.com>]

> I can think of a few workarounds, all bad:
> - add a partitioning tool (or option to qemu-img) to format the disk,
> placing the first partition on the fourth cylinder, aligning it.  tell
> the users not to wipe the disks out but instead install to one of the
> existing parititions

Well, that one slightly modified could work out quite well, at least for
linux.

As far I know the linux kernel uses the geometry provided by the storage
adapter only in case the disk is blank.  If there is a partition table
present on the disk, the linux kernel will calculate the geometry based
on that.

Background for this is that scsi disks have no disk geometry, they just
have a bunch of sectors.  The scsi hostadapter bioses have to pull out
some geometry out of thin air to satisfy ms-dos and real os boot
loaders, and there was no standard on how to do that.  Thus moving disks
from one scsi adapter to another may result in hba-reported and on-disk
geometry being different, and the only sane way to deal with that is
using the on-disk geometry.  With LBA this is much less an issue these
days though.

So qemu-img could create a partition table, containing one partition,
hinting 32 sectors/cylinder.  Linux should keep that geometry then, even
when distro installers are deleting the partition and creating their own
scheme.

Dunno how what *BSD or Windows guests will deal with that though.

cheers,
  Gerd