Understanding Device Interconnection - The Mac SCSI Debacle
SCSI
There
has been a long standing (and growing) hatred of the device connection protocol known as
SCSI (Small Computer Systems Interconnect) in the Macintosh world for many years. Even though
the earliest Macs included SCSI as the default device connectivity option, the combination
of non-hot-swap capabilities, device chain termination, cable length limitations, device
ID assignments, daisy chaining, and no fewer than 5 different connector formats and 6 different
currently used electrical specifications (SCSI 1, SCSI 2, SE, HVD, LVD, and SLVD) has made
utilizing SCSI in the Mac world a despised connection type to be avoided at all costs. Additionally,
with SCSI’s parallel, shared bandwidth design, we were also faced with the issue of device
data speeds either clogging the chain of devices, or requiring more bandwidth than even the
newest Ultra 320Mbs cards were capable of supplying.
SAS
A
new version of SCSI has been developed over the last few years called SAS - or Serially Attached
SCSI. SAS provides the answer to all of the problems mentioned above. Devices are hotpluggable,
require no user-supplied termination, are point-to-point and do not daisy chain, have much
more lenient cable lengths, do not share bandwidth, have their IDs assigned automatically,
and don’t require special consideration as to what type of device is plugged into what type
of card. Add to that 3Gbs and 6Gbs throughput options (full bandwidth is available to every
device), and SAS makes an outstanding device connection protocol for Mac systems for Disk
or Tape storage devices.
Current SAS host bus adapters (HBAs) are available from ATTO Technologies, LSI Logic, HighPoint Technologies, and Areca, If you're only connecting Disk to your Mac, all of these manufacturers products will work properly. However, only the ATTO Technologies and LSI Logic HBAs support tape drive connectivity. For PCI-E based Macs, we recommend:
- ATTO Technologies ExpressSAS H380
- ATTO Technologies ExpressSAS R380
- ATTO Technologies ExpressSAS H680
- ATTO Technologies ExpressSAS R680
(other ATTO ExpressSAS cards with proper connectivity also work)
- LSI Logic LSISAS3801E
For older, non PCI-E PowerPC Macs, LSI makes a PCI-133 (PCI-x) card:
- LSI Logic LSISAS3801X
