usb/da vs sata geometry calculations (was Re: Switchover to CAM ATA?)

Alexander Motin mav at
Mon Apr 26 13:07:57 UTC 2010

Andrew Reilly wrote:
> Was this the result of the umass/da driver having a different
> synthetic geometry calculation routine than the SATA driver?

ATA and SCSI disk drivers indeed have different geometry calculation
algorithms. ATA fetches geometry from DEVICE IDENTIFY data, while SCSI
seems just fakes them in many cases.

> This was all on an 8-STABLE system about 400 days old, fwiw.
> Should I expect any on-going badness as a result of this
> difference in "geometry" between two identical drives?

I hope not. LBA-aware loaders should use LBA offsets of the partitions,
which are not depending on geometry.

Alexander Motin

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