RE: small i & power systems (disk performance)

The performance difference between 3 and 4 drive RAID-5 Sets is pretty
noticeable. I would HIGHLY recommend never ever ever having a 3 drive
raid-5 set.

Pete

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Keith Carpenter
Sent: Thursday, April 24, 2008 5:08 PM
To: midrange-l@xxxxxxxxxxxx
Subject: Re: small i & power systems (disk performance)

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