Steen Linden wrote:

> > ahc0: aic7880 Wide Channel, SCSI Id=7, 16 SCBs
> > scsibus0 at ahc0 channel 0: 16 targets
> > ahc0: target 2 using 16Bit transfers
> > ahc0: target 2 synchronous at 10.0MHz, offset = 0x8
          ^^^^^^^^
  This is about a target device on the SCSI bus, not the SCSI bus itself

> Can someone explain why it is running at 10.0Mhz instead of 20Mhz? I

  That depends on the capabilities of the target device.  Here are some
examples:

  ahc0: aic7880 Wide Channel, SCSI Id=7, 16 SCBs
  scsibus0 at ahc0 channel 0: 16 targets
  ahc0: target 1 synchronous at 5.0MHz, offset = 0xf
  ahc0: target 4 synchronous at 10.0MHz, offset = 0x8
  ahc0: target 5 synchronous at 4.0MHz, offset = 0xf
  ahc0: target 8 synchronous at 20.0MHz, offset = 0x8

  These are all connected to the same SCSI bus.  Target 1 is an old
Conner harddisk (5 MHz, 5 MB/s max.), target 4 is a Fast SCSI tape
streamer (10 MHz, 10MB/s max.), target 5 is an old CD ROM drive (4 MHz,
4 MB/s max.), and target 8 is a new Ultra-Wide SCSI harddisk (20.0 MHz,
40 MB/s max.).  As you can see, the frequency is the maximum either the
controller or the connected device supports!

> and have not been able to locate any differences other than the firmware
> versions of the Adaptec and the disk.
                          ^^^^^^^^^^^^
  That's exactly what makes all the difference in your case.  Your
colleague's HDD obviously supports Ultra-SCSI while yours only supports
Fast-SCSI.

  Cheers
      ,
   Rene