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Rob,

Probably one of the most important aspect to performance is cache (I
guess you could say cash as well...ha ha ha), but that write cache really
does make a difference.

Each controller can support a max number of I/O operations per
second, if you go over that more arms doesn't help at all. If you are under
that max number, I would be a big proponent that more arms are best until
you reach that max number of I/Os the controller can handle.

We have taken 95 arms on like 6 or 7 4778 controllers, and went down
to 2 5780 controllers handling 26 disks, and had better performance. Of
course, these were different speed (RPM) disks as well, with better seek
time. So, technology does have a way of helping.

On your config, just think about this as you have a mixed capacity
ASP. If I want to keep all the disks in the ASP at 50%, I would have to
write twice as much to the larger 141GB disks then the 70GB disks, which
means on average twice as much I/O to those disks as the smaller ones. I
think its ok to have two different sizes, but you should never have 3 sizes
in an ASP.

JMHO

Pete Massiello

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of rob@xxxxxxxxx
Sent: Friday, September 14, 2007 9:16 AM
To: midrange-l@xxxxxxxxxxxx
Subject: Balancing the ASP

Added four drives on a brand new raid set. When I added them I selected
"Add units to ASPs and balance data". I am assuming this translates more
to STRASPBAL *CAPACITY than STRASPBAL *USAGE. Which, maybe, you really
have to start out that way at first. Left it that way for a couple of
weeks. Ended up with stuff like
Size % %
Unit Type (M) Used Busy
1 4328 141129 50.1 0
2 4328 105847 49.4 0
3 4328 105847 49.3 33
4 4328 105847 49.0 0
5 4328 105847 48.7 33
6 4328 141129 48.6 0
7 4327 52923 47.7 50
8 4327 52923 47.7 50
9 4327 52923 47.7 100
10 4327 52923 47.7 50

So I've decided to run TRCASPBAL from 8-4 today. When I go home I'll kick
off the STRASPBAL *USAGE and it will read the capture from the TRCASPBAL.
Hopefully that will help. I'll see on Monday...

Ok, I realize I mixed sizes in the ASP which is supposed to not really be
a performance enhancer. But the boss said they were quite cheaper.

I've been a big proponent of more arms is not necessarily better, and I
quote the fantastic performance improvement we got when we switched
development boxes and dropped from 42 arms down to 7, but something ain't
right here so we decided to pitch arms back at it.

WRKHDWRSC *STG
(Pertinent data pasted...)
Resource Type-model Status Text
CMB01 2844-001 Operational Combined function IOP
DC01 573D-001 Operational Storage Controller
CMB06 2843-001 Operational Storage Controller
DC04 571B-001 Operational Storage Controller

Resource Type-model Status Text
DC01 573D-001 Operational Storage Controller
DD004 4328-070 Operational Disk Unit
DD005 4328-074 Operational Disk Unit
DD006 4328-074 Operational Disk Unit
OPT01 6337-002 Operational Optical Storage Unit
D02 28DB-001 Operational Device Services
D01 180A-001 Operational Device Services
DD003 4328-070 Operational Disk Unit
DD002 4328-074 Operational Disk Unit
DD001 4328-074 Operational Disk Unit
D03 28DB-001 Operational Device Services
DC04 571B-001 Operational Storage Controller
DD007 4327-074 Operational Disk Unit
DD008 4327-074 Operational Disk Unit
DD009 4327-074 Operational Disk Unit
DD010 4327-074 Operational Disk Unit
D04 28B9-001 Operational Device Services
D05 28B9-001 Operational Device Services


Rob Berendt

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