#SCSI Problem.
Trent;
Beware! There is nothing wrong with Amy's SCSI-I reselection. It is the
drives that were in error. Thus, if you connect a SCSI-I drive to your
system, the potential is there for you to have reselect problems.
BTW, you example is one where you problem would not notice the difference
between reselection on and reselection off. AP does not hit the drive for
large transfers in each access. I am not certain but AP may only be
requesting or writing a few block at a time.
There are lots of parameters associated with the Amy's SCSI system that
will affect performance. Most of them are set for what is generally
optimal for reselection off, multiple drives present, moderately heavy
system load (multitasking) and moderately heavy DMA in use.
Under such setting as are "standard", setting reselection probably results
in differences that are only measurable but not perceivable. Also, the
faster the drive, the less difference will actually exist and of course
SCSI-II with SCSI-II drives will have a significantly smaller difference.
Though I am not recommending actually doing this unless you want to embark
upon a few days (weeks?) of careful testing:
You could increase the MaxTransfer and buffer settings dramatically. Then
play around with copying very large files (set copy's blocking size to
some attainable high value also).
Using activity of AP will not be valid for testing because AP appears
to be specifically "tuned" to insure that it does not interfer with
its own use of the serial port DMA. That is, it appears that Steve
took the appoach that he should set his disk useage such that he
would be able to keep up with the fastest and most demanding use of
the serial port but no more. Or in other words, he keeps his demands
for disk access to a small enough blocking factor to be "a good
neighbor" in a multitasking system.
-bill