neese@adaptex.UUCP (11/09/89)
I don't know about the WD algorithm for read aheads, but all of our controllers that have read ahead, except for the ACB-2322D, will abort read ahead on the receipt of a command. The abort takes place after the current sector read is completed. On a drive with 32 sectors/ track the maximum time a command will be held off is 520 micro-seconds. On a drive with 26 sectors/track, the maimum hold off time will be 640 micro-seconds. On a note about the comparisions, one comparison was done with ENIX and the other ISC 2.0.2. While I find the numbers useful and interesting, it should be noted that there is a dramatic difference between the filesystems of these two operating systems. ISC 2.0.2 has a fast filesystem, which means that larger multi-sector requests will be made, as compared to ENIX which uses the traditional SYSV filesystem. These requests will typically be 1K in size. I will soon have a system here, that I will be able to benchmark under ISC 2.0.2 and SCO 2.3/3.2UNIX. I will test the ACB-2372C (RLL)/ACB-2322B (10Mbit ESDI)/ACB-2322B-8 (15MBit ESDI)/AHA-154[02]A (SCSI). I plan to test the controllers with like drives (in physical design i.e. same number of heads/sectors per track) in like environments (i.e. same buffer cache size, clean filesystems). While I do not beleive that any benchmark is accurate in determining the real performance in a multi-user environment, the numbers should be good for static comparisons. This will take a while to get done, but when done I will post the results and the benchmarks (or code) that I used and the environment and settings for the buffer cache. Roy Neese Adaptec Central Field Applications Engineer UUCP @ {texbell,attctc}!cpe!adaptex!neese merch!adaptex!neese