Ours is designed the same, I asked the same questions and was given the 
following advice:

The alternative to specifying multiple database directories is to use hardware 
RAID controller or LVM to assemble multiple disks into a single 
filespace/directory,   You don't get the benefit of DB2's stripping when you do 
this, but what you loose is often made up for by the hardware's stripping.   
The other consideration is when doing this is that DB2 would normally throttle 
its I/Os going to the single directory (on the assumption that it represents a 
single disk), but there's a DB2 tuning parameter you can use to tell DB2 that 
the directory is backed by multiple disks, and to schedule its I/O accordingly. 
 In fact, TSM sets this parameter by default, so out of the box, DB2 will 
assume its database directories are backed by multiple disks

Rod

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of 
Andrew Carlson
Sent: Tuesday, May 11, 2010 3:45 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] TSM 6 database space performance question

It would probably not be a problem with it working, but with the two
lun's concatenated, there is probably little to no chance DB2 will be
able spread the I/O out among the 2 lun's.  If it's in a separate
filesystem, DB2 will spread the data out across them.  It will be even
worse with 3, 4, 5, or more lun's.

On Tue, May 11, 2010 at 3:21 PM, John D. Schneider
<john.schneider AT computercoachingcommunity DOT com> wrote:
> Greetings,
>   I have a customer running TSM 6.1.3 on a Linux RedHat 5.4 server.
> They are using high-performance SAN attached disk for the TSM database
> and logs.  They have created the TSM database all in one directory under
> one filesystem.  Recently then needed to add more space, and they carved
> out a lun from another RAID group, and then added that lun to the
> existing filesystem.  TSM shows that it now has the additional space,
> but it is still all under one directory.
>   In reading the Performance Guide and Admin Guide, they both recommend
> spreading the data out over multiple directories, putting each directory
> behind separate disks/luns.  This certainly makes sense to spread the
> I/O out over multiple luns, and I get that.  But is there anything wrong
> with the way my customer has done it?  They are using multiple luns from
> different RAID groups, but they are all put together behind one
> directory.  Is this going to become a problem as they add more and more
> load to this instance?  If TSM has lots of separate directories and they
> are across multiple luns, does TSM do it's database I/O differently?
>
> Best Regards,
>
> John D. Schneider
> The Computer Coaching Community, LLC
> Cell: (314) 750-8721
>



-- 
Andy Carlson
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