parameters on CDC Wren IV, Adaptec 1542b
Karl-P. Huestegge
karl at robot.in-berlin.de
Wed Nov 7 06:44:32 AEST 1990
bill at unixland.uucp (Bill Heiser) writes:
>larry at nstar.uucp (Larry Snyder) writes:
>>what you need to do is to change one item at a time - then
>>bench the system, change another - then bench, etc..
>Thanks for the feedback Larry. What utility are you using to do
>your benchmarking?
>>I have cache enabled (made a 10% difference) and changed the
>>buffer ratios from 4 to 16 (made a + difference on large disk IO,
>>and - on small; but since most of mine is large - I changed it)..
>I'm a little uncertain about the "buffer ratios" -- I didn't see any
>explanation of it in the lenghy aha1542 manual -- do you have anything
>that describes them? My "largest" disk IO activity is news processing
>(Cnews) and compiling software -- does that qualify as "large", and
>would you expect it to benefit from the increase in buffer ratios?
The Host Adapter has nothing to do with it - it's a SCSI-command.
The Buffer-Full Ratio and Buffer-Empty Ratio are part of the Mode Select
Command called the 'Dissconnect/Reconnect Control Page'.
The Buffer-Full (Buffer-Empty) Ratio indicates on READ (WRITE) operations
how full (empty) the buffer should be prior to attempting a reconnection.
The Quantum Prodrive Specs say:
Buffer-Full Ratio: During READ Operations, the drive disconnects when
the buffer is empty. The Value of the buffer-full ratio represents
the percentage of the buffer that must be filled, unless the buffer
contains all the required data, prior to reconnection of the drive
- that is, 255 (FFh) represents 100% full; 128 (80h), 50% full.
When the value is zero, the drive determines when it will initiate
reselection. The default value is 80h, indicating that the drive
will attempt a reconnection whenever the buffer contains at least
four kilobytes of data read from the disk.
Buffer-Empty Ratio: When the drive is disconnected during WRITE
operations, the value of the buffer-empty ratio represents the
percentage of the buffer that must be empty to enable
fetching data from the initiator, unless the buffer can hold
all the required data - that is, 255 (FFh) represents 100% empty,
128 (80h) 50% empty. When the value is zero, the drive determines,
when it will initiate reselection. The default value is 80h,
indicating that the drive will attempt a reconnection whenever
the buffer contains at least four kilobytes of data transferred
from the initiator.
--
Karl-Peter Huestegge karl at robot.in-berlin.de
Berlin Friedenau ..unido!fub!geminix!robot!karl
More information about the Comp.unix.sysv386
mailing list