Re: small i & power systems (disk performance)

[Keith Carpenter <entropypool@xxxxxxxxx>]

ChadB@xxxxxxxxxxxxxxxxxxxx wrote:
> The new DASD and cache oriented controllers are very good performers.  The
> integrated 5727 controller has done very well for us on both DB2 based
> systems and WAS/Domino setups.  If at all possible, see if your business
> partner can get some modeling done for you by Randy Watson's company
> Midrange Performance Group (you can collect a period of current performance
> data, easily send it to them, and they can send you 'What If' modeling back
> against various blends of controller/disk setups.  If your BP doesn't work
> with MPG as a service, I think MPG also will sell you this service at a
> pretty reasonable price (getting the right hardware spec'd with some expert
> assurance based on hard data can be pretty valuable).  The only thing i've
> heard to really watch out for still is 3 drive RAID setups... that may have
> been fixed in the last year or two, though.

BP had us load MPG's Performance Navigator on PC.  Makes it easier to 
download the collected data for the BP.

The 3 drive RAID5 set issue is not unique to i.  RAID5's weakness is on 
data writes where the parity needs to be calculated and written as well. 
 With 3 drives, 1/3 of the write operations are parity.  With larger 
sets this parity write overhead goes down.  A large cache controller 
helps, but it's probably cheaper to just add more disk.


Keith