ITEM: E1964L

Questions about disk I/O pacing.

Question:

I have an application that performs many read and write operations.  I
believe that there is a bottleneck at my disk drive.  I find my cpu often
entering wait states - perhaps to access the disk.  I understand that
I/O pacing is a way to ease the bottleneck.

I would like some more information on disk I/0 pacing.  I understand
that there are two values that can be set - maxpout and minpout.  
What exactly do maxpout and minpout set andwhat are some good numbers to
try setting them at?

Response:

    Disk I/O pacing sets up a high and low water mark for writes to a file.
It will suspend processes writing to the file when the number of outstanding
I/O requests is above the high water mark.  These processes (and any new
processes that write to the same file) will remain suspended until the queue
gets to the low water mark.  This will allow processes doing less
frequent disk accessing to be able to get quicker response from the
disk.  You should try values around 17 for maxpout and about 5 for
minpout.  You can play around with these, trying values higher and
lower to tune the I/O pacing to what your needs are.




Support Line: Questions about disk I/O pacing. ITEM: E1964L

Dated: October 1993 Category: N/A

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