[9fans] DPT controllers (Was etherelnk3.c)

[9fans] DPT controllers (Was etherelnk3.c)

[Mark]

In comp.os.plan9 it was written:

>>>When PCI finally settles down and gets as reliable as 154x's on
>>>the ISA bus, I'll move.  Of course a good SCSI adapter design
>>>would be nice.  I hate the 294x.  Does anybody have any experience
>>>with the Qlogic board?  (http://www.qlc.com)  It looks like
>>>a good alternative.
>>i know of drivers available for 3 other controllers:
>>	buslogic (mylex)
>>	dpt
>>	ncr (symbios) 53c8xx series
> But how do those controllers compare to the Qlogic board or
> the Adaptec 294x?

The DPT controller is the only one that supports RAID, with the added bonus
of up to 64MB of Cache.

> The QLogic board has two processors like the 154x and you only get one
> interrupt per SCSI command. (like the 174x. you can get many completed per
> interrupt on the 154x.) The 2940 gives interrupts as targets
> disconnect/reconnect! The host processor has to almost manage the SCSI bus
> directly. A 154x will even retry a command to a BUSY LUN for you without
> issuing another interrupt.

The DPT controller creates one interrupt per a completed command (this may
entail several SCSI commands on the bus, or partial commands due to the
Cache or elevator/coallesce optimizations). The DPT controllers (and the
processor used on the board) supported by John Chmielewski's driver are:

	Board	 Proc	# of Buses
	PM2024	 68000	1
	PM2124	 68020	1
	PM2124W	 68020	1
	PM2124UW 68020	1
	PM2124UN 68020	1
	PM2044W	 68000	1
	PM2144W	 68020	1
	PM2144UW 68020	1
	PM3224	 68030	1
	PM3224W	 68030	1
	PM3334UW 68040	1-3
	PM3334UW 68040	1-3
	PM3334WD 68040	1-3

All DPT controllers automatically perform retries on DASD type devices,
and will, if in a RAID configuration, run the array as degraded based on
devices failures. The PM3334 series of boards handles HOT swapping of
drives, but all the controllers can maintain a HOT spare drive with
automatic array rebuild on drive failure.

> On my systems I like to have as many SCSI busses as I can so I can have a
> reasonable number of targets per bus.  So having many cards that need to be
> patted on the butt every time a target blinks is not good for getting any
> other work done, like servicing ethernet clients.

You can put 45 drives on *one* PM3334 if you want ...

> I can put 4 154x's in a system with a P5/133 and have plenty of CPU to keep
> the ethernet lit.  How many 2940's can you run with a P5/133 with targets
> disconnecting/reconnecting like crazy because of all the random I/O?

I don't know, DPT (officially) doesn't own any Adaptec cards :-) ;->

All the above DPT PCI cards do circles around the 154X series of cards. In
fact, our lowest end ISA based controllers (I know, John's driver doesn't
support them, but it can since there is no difference to the interface
ports and command sets if you force the I/O addresses) are 40% faster than the
2940s and none of our cards are as slow as the 154X's as well!

But then I am biased ...

Sincerely -- Mark Salyzyn