Same number of LUNs in fewer VGs, or fewer LUNs, too?  The queuing concern
makes it sound like fewer LUNs.  If so, as Rick says, that's also where your
I/O concurrency would suffer.

If it's the same number of LUNs, using one VG per LUN makes it easier to
isolate each LV to each PV rather than potentially mixing them all together,
possibly having multiple LVs share the same PV, which could result in
database I/O to different DB2 volumes hitting the same PV and causing extra
contention.  (To be fair, in modern SAN arrays, the consumer host has no idea
where any of the blocks really live in the back end, so that kind of
contention can and probably often does happen anyway.)

My gut reaction with DB2 on TSM 6 and up is that nothing with the database
layout is as easily fixed as it was with the embedded database in TSM 5 and
earlier...  :-/  There's always trade-offs...

=Dave


On 07/15/2015 09:15 AM, Rhodes, Richard L. wrote:
> The concurrency I'm aware of is at the hdisk/lun level.  There's a 
> num_cmd_elems at on the fcs adapter which we set to 2k, and then queue_depth 
> on the hdisk.  That's why spreading I/O across as many hdisks/luns as 
> possible is advantageous.
>
> Rick
>
>
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of Huebner, Andy
> Sent: Wednesday, July 15, 2015 9:33 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: Disk layout for AIX
>
> He claims there is a queuing issue with too many at the HBA.  I guess I 
> missed that the last 12 years of being a storage/TSM admin.
> I told him the theory of using many was to allow more concurrency.  Before we 
> build I just want make sure this is not a mistake that cannot be easily fixed.
>
> Thanks,
>
> Andy Huebner
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of David Ehresman
> Sent: Wednesday, July 15, 2015 8:12 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Disk layout for AIX
>
> VGs are cheap.  Why does your AIX admin want to reduce the number of VGs?
>
> David Ehresman
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of Huebner, Andy
> Sent: Wednesday, July 15, 2015 9:03 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: [ADSM-L] Disk layout for AIX
>
> I have an AIX admin that wants to build my new TSM server using two VGs for 
> the database (6 file systems) and one VG for the various logs.
> We currently have 6 VGs for the DB and 3 VGs for the logs.  Each VG contains 
> 1 file system.
>
> The DB is about 375GB and the new hardware is a P8.
>
> No TSM de-dup.
>
> Should I be concerned about the DB setup?
>
>
> Andy Huebner
>

--
Hello World.                                David Bronder - Systems Architect
Segmentation Fault                                      ITS-EI, Univ. of Iowa
Core dumped, disk trashed, quota filled, soda warm.   david-bronder AT uiowa 
DOT edu