IBM FC #4319 disk drives
I have 25 4319 10k 35gb disk drives in a closet my management would like to have added to the existing iSeries. My question is if I replace FC#4318 10k 17gb drives with FX#4319 10k 35gb drives will performance degrade?
How or where can I find the seek times, MTBF numbers etc to compare performance?
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ASKED:
January 18, 2006 2:03 PM
UPDATED:
January 19, 2006 12:03 PM
Answer Wiki:
Hi,
As a rule of thumb I usually have a look at the number of disk drives and the number of IOPs the disk drives are attached to. Then I have a look at the type of work the disk drives are mostly performing - more reads or more writes. Most of this can be determined from performance reports.
But if you are replacing the same number of disks - 25 17Gb with 25 35Gb on the same IOPs doing the same type of work and balancing the disk drives then you should have the same performance with about double the capacity. If however the rules change you will have to do some proper planning.
Good luck
JohnDavid
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Seek times and MTBF numbers for these two types of drives are about the same. I have over 100 of the 35gb drives and average about one failure every 6 or 8 months.
There is a command you can use that will give you an idea if performance will be a problem. It is WRKDSKSTS. There is a column titled % busy. As a rule, this number should not exceed about 30%. I would suggest taking a couple of 15 minute samples at different time of the day to see what your current number is. If you plan on doubling the capacity of the drives you want this number to be less than 15 to 20 percent with the 17bg drives.
Hope this helps.
My reference has been the system report from performance tools to determine how busy your current drives are. The operations per second on the drives should not exceed 30 on average per drive. It also depends on the IOP you have and how many drives you have on the IOP and the application that’s running on the system. The drive information can also be found on on the system report. If ops per second exceed 30 or are close, adding higher capacity drives on the same IOP will only make matters worse. If this is the case, I would suggest investing $900.00 for a higher cache IOP for the drives and that will alleviate some of the performance botleneck.