Single large LUN or multiple smaller ones



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  • 5. AIX LUN Size
    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 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?

Single large LUN or multiple smaller ones

Postby rodak » Sun, 13 Feb 2011 05:14:23 GMT

I have a Power7 model 770, connected to EMC DMX/Symmetrix SAN via 8GB
FC (using NPIV) to 2GB SAN fabric.

From an AIX performance standpoint, is there any advantage to creating
a volume group from several smaller LUNs versus a single large LUN?
We're talking about less than 1TB, total.  This is for Oracle 10g, if
that makes a difference (and my DBA has already said he wants standard
filesystems - he doesn't want to hassle with using raw logical disks).

Re: Single large LUN or multiple smaller ones

Postby Johnny Rebel » Sun, 13 Feb 2011 06:01:24 GMT

I guess it depends on how the back end is configured.  A DMX I connect
to uses metaluns to put LUNs together in the Invista layer.  Testing for
me showed striping, mirroring etc.. anything on the AIX side greatly
reduced performance.  We moved from a striped VG, to a concatenated
(invista concatenation and then just built the vg using the LUNs with
nothing fancy) one.  The difference for me is invista, and/or how the
SAN storage is configured.  Ideally for Oracle of course (mine has
Oracle on it) you want R10 - wherever it may be.

Best bet if you are able is to test out various configurations with
iozone (this is how I found a SAN R10 bucket misconfiguration on the SAN
side... ).  I took a few days to do this and map it out, and it paid off.




--> GNU/Linux is user friendly... it's just picky about its friends.

Re: Single large LUN or multiple smaller ones

Postby Hank M. Higher » Sun, 13 Feb 2011 15:59:51 GMT

raw disks are not recommended anymore by oracle, but are considered a
"historical anomaly" now.
BUT oracle ASM (automatic storage management) provides both filesystem
and volume manager functions taylored to the DBMSs needs (includes
striping with different strip sizes for different file categories as
well as the ability to configure preferred mirror copies for reading).
things you cannot do with jfs2 nor gpfs. If you're serious about oracle
performance, look at ASM. the DBA will need to brush up his skills


Re: Single large LUN or multiple smaller ones

Postby Uwe Auer » Thu, 17 Feb 2011 03:47:03 GMT

Am 11.02.2011 21:14, schrieb rodak:


still true: Use more smaller than few large disks and proper LV settings 
(maximum inter policy). Don't believe arguments telling "In nowadays SAN world 
LUN size doesn't matter". Bad experience, poor performance.
In your example of a 1 TB database I would accept 128 GB disks but our choice 
would be 64 GB disks.


Re: Single large LUN or multiple smaller ones

Postby Johnny Rebel » Thu, 17 Feb 2011 11:08:57 GMT

While I would agree with you in most cases, I would argue against with
EMC invista - the testing I did showed using the tried and true way
(many smaller disks...) gave us a pretty {*filter*} hit on performance.
Using concatenated meta luns was far superior.  Old Shark on the other
hand, we were doing 35G luns (and lots of them). :)



--> GNU/Linux is user friendly... it's just picky about its friends.

Re: Single large LUN or multiple smaller ones

Postby niella » Fri, 11 Mar 2011 05:01:07 GMT

Absolutely. Using LUNS that are too large (or that are configured with
a too small queue depth settings) will result in queuing at the
logical disk level - you will observe non-zero values for sqfull in
the output of iostat -aD. For maximum performance, you should be using
scalable volume groups with smaller sized LUNS, say 64 - 128GB in


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