apples wrote:
> Sorry for posting this here but I never got any feedback in the storage
> group....
>
> 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 don't know of any performance benefits to using smaller luns, but
there are other considerations (Mostly application related). For
database environments, how do you back up a 1TB pool with one database
on it inside a timely window? (Or restore it for that matter?) Disk
hotspots are easier to deal with when you can shift components of the
database or application into different sets of smaller luns. The IBM
sales guys might say you don't have to worry about 'hot spots' on an
ESS, but the right combination of DBA neglect and developer bloat can
drag any SAN disk system to its knees...

> 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.

As far as performance, no there's no real benefit these days to jamming
more disks into a raid or virtual disk. You have a largish cache on the
SAN controller that throws the old religion out the window (IE, more
spindles doesn't directly give you more performance in a SAN worth it's
beans). Instead of playing ring-around-the-raid, you'll be playing
whack-a-mole with Fibre Channel throughput and array contention with
other systems on your ESS. If you're curious about performance of
different RAID configurations within the ESS you might check out this
IBM benchmark doc on ESS. It's focused on Oracle, but has good numbers
on RAID performance within the ESS:
http://www-03.ibm.com/servers/storag...id5-raid10.pdf

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

LUN disk queues? Not sure what you mean by that, however having the
ability to size luns to anything you want just gives you more control.
However, there are still plenty of reasons to keep small lun sizes
instead of just tossing a 1TB pool at the OS (As stated above). If the
application you support really wants 40GB volumes instead of 36GB (32GB
usable) then you can just request your san group give you 40GB vols
instead of you wrangling multiple disks into the sizes you need.