Data Storage - LUN Size

Author

LUN Size

apples

2005-10-24, 9:43 am

I have enterprise class storage (ESS800) and some lower-end fastt900
storage connected to AIX and Windows hosts.

Is there any benefit in creating smaller LUN's vs bigger LUN's when
connecting an AIX server to the ESS (or FAStT).

I was always lead to believe that the more hdisks the better since you
get more spindles and disk queues. If I create 5 LUN's or 10 LUN's from
the SAN storage then in both cases I may use the same number of
physical disks. So I'm not getting in more physical disks or spindles.
What about disk queues - I'm getting more of them when I create smaller
LUN's but I'm not really sure what (if anything) that is doing for my
performance.

Can someone explain the connection between LUN disk queues and phsical
disks - what do they really mean?

brian.mitchell@trx.com

2005-10-24, 9:44 am

At work, I admin both IBM products: two ESS-800 ("Sharks") and
multiple FastT700 (DS4400) (in addition to HP and Network Appliance
systems) so I may be able to assist...

Here's the deal: With larger-and-larger controller cache sizes,
fibre-channel subsystems, and storage virtualization within modern disk
arrays, worrying about disk queues and more spindles is only for the
very specialized shops that wish to squeeze every single drop of
performance out of their block-level SANs; So that throws the old
religion of "more-spindles-equals-more-performance" out the window.

There's also no direct answer to your question, it's more about the I/O
behavior of your applications (Are there lots of random read/writes or
sequential reads? What kind of workloads are we talking about? Are
you aware of any hotspots on your SAN? Do you using RAID-5 or
RAID-10?)

Email or call me if you want to further discuss the issue...

Brian J. Mitchell
Systems Administrator
TRX
6 West Druid Hills Drive
Atlanta, GA 30329-2158 USA
http://www.trx.com

email: brian.mitchell@trx.com
office: +1 404 327 7238
mobile: +1 404 725 3128