neese@adaptex.UUCP (10/20/89)
>/* ---------- "Seagate ST01/02 SCSI Controllers --" ---------- */ >Why are Seagate SCSI controllers so much cheaper than others, >such as WD or Adaptec? The Seagate board, which is a derivative of an older Future Domain design is a very general purpose SCSI adapter with a minimum amount of intelligence. With only 3 or 4 chips on the board, it can be made very cheaply. The WD/Adaptec adapters are intelligent SCSI host adapters that really take advantage of the SCSI bus. Requiring a lot more IC's and firmware. >A friend told me that the Seagate >boards take over the bus during transfers, and that while this >makes the boards very fast, it causes problems under multitasking >operating systems. Is this right? The Seagate board is a PIO/DMA device. It does not move data for the CPU. The WD/Adaptec boards do. The problem under multi-tasking operating systems with the Seagate card is due to the lack of intelligence. The driver in the UNIX/XENIX kernel has to do all the work for the card. The hardware has no provisions for multi-threading. This makes it very difficult to multi-thread as there are some timing requirements that must be met in order for multi- threading to work properly. It is very difficult for UNIX/XENIX to do this as they are not real-time operating systems. >While hard disk transfers are going on, can interrupts be missed? While PIO transfers occur the CPU can't do anything else. If a device such as the dumb COM ports do not get serviced quickly enough, data will be lost as they have very small hardware buffers. >If anyone knows about problems when using these cards under, say, >Unix, I would like to know about them. If I have a choice between the Seagate card and a 1:1 MFM controller, I would rather use the MFM controller. This is again due to the difficulty with writting a device driver for UNIX/XENIX that has severe timing requirements. >It sounds like there shouldn't be trouble under Dos. Agreed. >Alternatively, is there much of a difference in performance between various >SCSI cards? I had thought that the performance would be fixed by the SCSI >device regardless of host controller, but I'm not sure. You are partially right. Data transfer rates are regulated by both the adapter and the device. If the host adapter cannot generate ACK's/REQ's fast enough The adapter will limit the transfer rate possible from/to the SCSI device. For instance, a Conner SCSI drive would perform about the same on the Adaptec AHA-1540A and the Seagate card. As the drive is very limiting on the rate it can transfer data. On the other hand, a Quantum PRO40/80S drive will only yeild about 1.2MBytes/sec on the Seagate card and 2.6Mbytes on the AHA-1540. The bottom line is, how fast do you want your SCSI to be. You can make it as slow as a good MFM controller/drive or more than twice as fast as a fast 1:1 ESDI/drive combination. In the case of SCSI you definately get what you pay for, as far as performance goes. Roy Neese Adaptec Central Field Applications Engineer UUCP @ {texbell,attctc}!cpe!adaptex!neese merch!adaptex!neese
ching@pepsi.amd.com (Mike Ching) (10/21/89)
In article <6100018@adaptex> neese@adaptex.UUCP writes: > For instance, a Conner SCSI drive would perform about the same on >the Adaptec AHA-1540A and the Seagate card. As the drive is very limiting >on the rate it can transfer data. On the other hand, a Quantum PRO40/80S >drive will only yeild about 1.2MBytes/sec on the Seagate card and 2.6Mbytes >on the AHA-1540. Wish I could come close to that with my ST02/ST225N combination. Coretest says I'm only getting 138KBytes/sec compared to 250KBytes/sec from my 2:1 interleaved MFM controller and a ST4038. You definitely get what you pay for in this case. mike ching
c60a-1bd@e260-1g.berkeley.edu (Jeff Davis) (10/22/89)
Hello, Talk of st01 and st02 controllers has made me curious about my current setup. I have an ST-02 controller with and st296N 80meg seagate drive. The current transfer rate according to the core test is in the neighborhood of 320k. The drive also has REV 8 roms which I have heard are slower than rev. 7 ones (it was slowed down for the MAC is the claim I have seen.) My question is What kind of performance can I expect if I can get rev 7 roms for the drive? Also what about a better controller? I plan to run UNIX when I get the money so I was looking at the Adaptec controller. Will it work with the seagate drive? -- Jeff Davis (JCDavis@LBL.GOV)
neese@adaptex.UUCP (10/26/89)
> Talk of st01 and st02 controllers has made me curious about my current >setup. I have an ST-02 controller with and st296N 80meg seagate drive. >The current transfer rate according to the core test is in the neighborhood >of 320k. The drive also has REV 8 roms which I have heard are slower >than rev. 7 ones (it was slowed down for the MAC is the claim I have seen.) >My question is What kind of performance can I expect if I can get rev 7 roms >for the drive? Also what about a better controller? I plan to run UNIX >when I get the money so I was looking at the Adaptec controller. Will it >work with the seagate drive? The AHA-1540A/1542A will work with the Seagate drive. Performance won't be that great, but it will work. I might as well throw this in while I am at it. The single biggest reason the ST02 card can't run the Seagate drive at 1:1 interleave is the Seagate drive does not have a read ahead buffer on it. If it did, then 1:1 would be maintainable. If you are looking for a SCSI drive and want some performance, then you must look for drives that have a read ahead buffer or else you can't maintain a 1:1 interleave, no matter how fast the system is, as long as you use the ST02 card. The 1540 can maintain a 1:1 interleave on drives that don't have a read ahead buffer, so you would gain that. Roy Neese Adaptec Central Field Applications Engineer UUCP @ {texbell,attctc}!cpe!adaptex!neese merch!adaptex!neese