On Sep 11, 2:04*pm, Patrick Finnegan
wrote:
> On Sep 10, 9:10*pm, Hajo Ehlers wrote:
>
> > > We are using JFS with no striping cos MWC is turned on but does MWC
> > > mean anything on a SAN?

>
> > Back to the basics:
> > What are you trying to archive anyway. ?
> > Do you have any performance issues ?

>
> We have a DB2 database performance issue that is related to slow disk
> i/o times which could be caused by a technical issue with the SAN or
> simply by contention if for some reason the data is clustered on one
> small area of the san. *We have to prove that there is a problem
> before the Management Company who look after the san will allocate
> resources to look at the issue. *Working on the principle that we will
> get the best performance by allocating the data over as many disk as
> possible we were wondering whether the AIX system utilities would give
> us any worthwhile information about how the data is distributed on the
> san but it looks like they don't so we will have to escalate up the
> management chain.
>
> The disks in the SAN are raid 5 so the logical volume MWC setting is
> probably irrelevant.



Here are the DB2 I/O stats for writes to the logs and databases.
Looks pretty slow to me.


Production.
*********

Log write time (sec.ns) = 33228.000000004
Number write log IOs = 14813312

(33228.000000004 * 1000 ) / 14813312 = 2.24 milliseconds per
write.

Direct write requests = 336397
Direct write elapsed time (ms) = 3799167

3799167 / 336397 = 11.29 milliseconds per write.