At 10:24 AM 2/12/98 -0500, Gary Feinstein wrote:
>       By usage, I assume you mean %busy?  My usage is roughly 4% on each
>drive. Although, this is probably so low due to the lack of heavy
>processing right now. I just added another 30Gig DASD bringing me to a
>total of 60Gig.  All disks are in a RAID5 array.  My original 16 are 2Gb
>each, the new drives (8 of them) are 4Gb.  It looks like the data is
>still being written to the new disks...half are at 90%, the others at
>30%.  Will this have an big effect on my processing?


Right. I was referring to the disk actuator activity. The activity should even 
out eventually, but in the mean time, if the disk is busy 90% of the time, that 
means that only 10% of its requests are processed immediately. That will 
undoubtedly have some impact. Unfortunately, the only real "cure" for this is 
to do a complete save, scratch the disks and restore. Not a pleasant prospect. 
I've had some success with allocating enough space to almost fill the new DASD 
to the same level as the old drives, and then over a period of a few weeks, 
gradually decreasing the allocated space. This seems to help spread the 
disproportionate activity somewhat. If you allow the system to run unchecked, 
the excess activity on the new drives will tend to concentrate your most active 
data there. It will still even out, but it will take longer to do so.


Pete Hall

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