Are SCSI-3 hard drives and/or controllers available yet?
Allegedly. Previous postings have said "I heard that SCSI-3 has been standardized," but I haven't seen anything firm about it. I've seen controllers advertised by JDR Microdevices and some cheap clones; the Quantum "Empire" drives are also advertised as SCSI-3 by some mail order vendors. Seagate and IBM call their fastest drives (probably comparable in speed to the Quantums, if not faster) "Wide SCSI-2."
That's a misnomer. See below.
What is the difference between SCSI-3 and Fast & Wide SCSI-2?
Wide SCSI-2 required two cables to do 16 bit wide transfers. SCSI-3 defined a single cable, single REQ/ACK 16 bit wide transfer. The reason you are hearing 16-bit single cable being called SCSI-3 is that they CAN. The fact that single cable 16-bit has been around for a while just shows you how much the standardization process lags behind the real world.
SCSI-3 is really a family of standards. SCSI was broken up from a single document into different layers and command sets. This was done to allow for different physical transport layers (like fibre channel and SSA) to be defined, and to allow for smaller "bite-sized" projects that maybe get done a little faster ;-)
The family includes the following members with TLAs:
After perusing the latest issue of Computer Shopper, I came away with the impression that companies are calling F&W scsi-2 hd's SCSI-3. Is this an incorrect assumption, or is F&W SCSI-2 known as SCSI-3? Is this really mostly marketing hype?
Actually, there is something to that. TECHNICALLY, what is out there is often a hybrid: SCSI-3 "SPI" silicon with some other hodgepodge of SCSI-3 proposals, all mixed in with SCSI-2 stuff.
An earlier posting said that the Quantum Empire ("SCSI-3") drives contain some commands from the SCSI-3 command set, and Adaptec suggested a specific setting on its 2940W controller to work properly with the drive.
I understand there are some drives with proposed SCSI-3 command features. These are mostly in the MODE SELECT and in error codes, as I recall. Perhaps someone who knows more about this could elaborate?
Note also that the major players (like DC Drives) don't have any "SCSI-3" stuff advertised; only JDR and some cheap clones are promoting it. Besides, Wide SCSI-2 has yet to really catch on (mostly because only a few drives are fast enough to take advantage of it).
There is no "wide SCSI-2" because that would mean two cables. Single cable wide SCSI has always been SCSI-3, it just took too d*** long to get into a standard!-)
I've seen a few comments about our 54C90 being faster than spec. While I doubt the author was really complaining (I got twice as much as I paid for--sure makes me mad ;-) I'd like to explain the situation.
Along the way, I'll also show that asynchronous is faster on short cables, while synchronous is faster on long cables. The cross-over point occurs somewhere around six feet--assuming that you have our 53C90 family devices at both ends of the cable. The reason has to do with the propagation delay of the cable; the turn around time of the silicon; and the interlocked nature of the asynchronous handshake.
First REQ goes true /* driven by Target */
then ACK is permitted to go true /* driven by Initiator */
then REQ is permitted to go false
then ACK is permitted to go false
(4 * 1.7 * 1) + (4 * 40ns) = 167 ns /* 1 foot cable */
= 6 MB/s
(4 * 5.25 * 6) + (4 * 40ns) = 286 ns /* 6 meter cable */
= 3.5 MB/s
(4 * 5.25 * 25) + (4 * 40ns) = 685 ns /* 25 meter cable */
= 1.5 MB/s
Our simulations say that under very best conditions (fast silicon, low temperature, high voltage, zero length cable) we can expect more than 8 MB/s asynchronously. In the lab, I routinely measure 5 MB/s on 8 foot cables. So, if you were writing the data manual for this, how would YOU spec it?
The framers of the SCSI spec threw in synchronous mode to boost the performance on long cables. In synchronous mode, the sending device is permitted to send the next byte without receiving acknowledgment that the receiver actually received the last byte. Kind of a ship and pray method. The acknowledgment is required to come back sometime, but we just don't have to wait for it (handwave the offset stuff and the ending boundary conditions). In this mode any external transceivers add a time shift, but not a delay. So if you negotiate for 5 MB/s, you get 5MB/s regardless how long the cable is and regardless whether you are single-ended or differential. But you can't go faster than 5.5 MB/s, except in SCSI-2. Synchronous mode does have a hold time (unlike asynch) but again, setup and hold times subtract out. In SCSI-1 synchronous mode, the speed limit comes from the combined ASSERTION PERIOD + NEGATION PERIOD which is 90ns + 90ns = 180ns = 5.5 MB/s. Our 53C90 family doesn't quite hit the max, but we do guarentee 5.0 MB/s. In SCSI-2, anything above 5.0 MB/s is considered to be FAST. Here the maximum transfer rate is explicitly limited to 100 ns or 10MB/s; you don't have to read between the lines to deduce it.
Interesting tid-bit: given a SCSI-2 FAST period of 100 ns and a cable delay of 131 ns on a 25 meter cable, you can actually stack 1.31 bytes in the 8-bit cable. In FAST and WIDE SCSI you can stack 5.24 bytes in this copper FIFO. Hummm...
The drives are shipped with SCSI ID set to 7. To select a different ID refer to the following:
Table A Table B ID E-1 E-2 E-3 ID E2 E3 E4 ================== ================== 0 out out out 0 out out out 1 in out out 1 in out out 2 out in out 2 out in out 3 in in out 3 in in out 4 out out in 4 out out in 5 in out in 5 in out in 6 out in in 6 out in in 7 in in in 7 in in in
For the CP 340, jumper E-1 to disable parity.
All other models, jumper E-4 to disable parity.
SCSI drive parameters:
Model Hds Cyl Sec Table LED
===========================================
CP2020 2 642 32 A n/a
CP340 4 788 26 B 1
CP3020 2 622 33 A 1
CP3040 2 1026 40 A 1
CP3180 6 832 33 A 1
CP3100 8 776 33 A 1
CP30060 2 1524 39 A 2
CP30080 4 1053 39 A 2
CP30100 4 1522 39 A 2
CP30200 4 2119 49 A 2
CP3200 8 1366 38 A 2
CP3360 8 1806 49 A 2
CP3540 12 1806 49 A 2
CP 30080E 2 1806 46 AA C/E
CP 30170E 4 1806 46 AA C/E
CP 30540 6 2249 59-89 AA B
CP 31370 14 2094 59-95 AA B
LED 1 LED 2
J-4 Pin 1 = + J-1 Pin 3 = +
Pin 2 = - Pin 4 = -