sl@van-bc.UUCP (Stuart Lynne) (10/14/89)
I'm evaluating an Adaptec 1542 SCSI controller with a Miniscribe 3130 SCSI drive under SCO Xenix 2.3.2 GT. This is in a 25Mhz 386 box from Monolithic Systems (a pretty generic C&T style board, no cache). So far the results are pretty dismal. Just over 100kbps throughput. I've patched the kernel ad_xfer to 1 for 6.7Mbit DMA and setup the board in various ways. The 386 is running at 25Mhz, with the bus at 12.5Mhz and the DMA clock at 12.5Mhz. I use a simple test for timing the effective throughput for reading: time dd if=/dev/device of=/dev/null ibs=100k obs=100k count=100 My WD1006SR2 on the same system does the above in about 25 seconds for the raw device, and 26 for the cooked device. The Adaptec does it in about 94 seconds for the raw device and 180 for the cooked device. I've also tried a CDC SCSI drive with precisely the same timing results. Is this normal or do I have things setup wrong? -- Stuart.Lynne@wimsey.bc.ca ubc-cs!van-bc!sl 604-937-7532(voice) 604-939-4768(fax)
neese@adaptex.UUCP (10/20/89)
Using 'dd' to measure throughput will not give you much idea of the real
overall benefits of the 1542A.
The real benefit of the 1542A is realized when you measure the overall
load on the AT bus or how much time the CPU spends messing around with
disk I/O instead of doing what it should be doing,....spending time on user
processes. Try starting a 9600 buad communication process on a dumb COM
port and then start up some severe disk I/O. You will find that MFM/RLL/ESDI
controller/drive combinations will cause occasional character loss, while
the 1540A in the same situation will not.
The Miniscribe drive is also limiting the speed at which things will occur.
It is an unfortunate fact that the best SCSI adapter you can use will be
directly impacted by the SCSI device you chose. The best devices I have
found to date are the Quantum PRO40/80, CDC (any Wren after III, with read
ahead enabled), and Maxtor XT series of SCSI drives w/read ahead enabled.
You may also want to patch 'ad_buson' and 'ad_busoff'. They are currently
set to 5 on and 7 off. I recommend 6 on and 8 off in conjunction with
the setting to 6.7MBytes/sec data rates. You should also install the
J1 pin pair 1 jumper to enable synchrounous transfers.
I also do not recommend the Seagate, Rodime, Conner, Priam, Miniscribe,
and Micropolis. Not for reliability, but for performance and overall
SCSI bus usage.
Roy Neese
Adaptec Central Field Applications Engineer
UUCP @ {texbell,attctc}!cpe!adaptex!neese
merch!adaptex!neese