Re: STRASPBAL on guested partitions

Rob,

I'm wondering if the guest OS in use makes a difference.

It seems to me that IBM i, unlike other operating systems, was
designed (optimised?) for a RAID 0 environment. The OS expects to be
able to spread a file across multiple disks. Whereas Linux/AIX
expect to see the file on a single logical drive.

But I'm surprised that STRASPBAL *USAGE is ignore on the guested
LPAR. That must mean that the guested i OS must somehow know it's
disks are virtualized. If so, then I guess the OS could have
additional optimizations for a single large virtual disk.

Charles

On Fri, Jul 24, 2009 at 10:04 AM, <rob@xxxxxxxxx> wrote:

Sometimes I wonder if a little knowledge of how Linux on Power works would
help to understand this.  We used to use Guested Linux.  (Now we use
dedicated lpars.)  One guested lpar had numerous virtual disks (it was
growing by leaps and bounds).  There was some reason why we went through a
lot of effort to reduce the number (wasn't my task).

With a guested lpar, if your host has 90 disk arms, I would think that
your guest could then potentially share all 90 arms (depending on how
single level store scatters the data).  Versus a dedicated partition that
has to have a section carved out with x number of arms, controllers, etc.

I don't know how multiple versus a single virtual disk plays into this.  I
was rather hoping that it wasn't a performance concern one way or the
other.  Hoping that all that would have been simply dumped onto the
hosting machine.

Granted, if STRASPBAL *USAGE is ignored by a guested lpar than what
happens when run on the hosting lpar?  For instance, let's say file XYZ on
GUEST is heavily used.  Now let's say you have two virtual disks
associated with GUEST.  So when you run STRASPBAL *USAGE on HOST how would
it know that file XYZ on GUEST is heavily used?  It wouldn't.  What it may
know is that
/QFPNWSSTG/GDISTG01
or
/QFPNWSSTG/GDISTG02
or both, is heavily used and scatter that around?

Rob Berendt
--
Group Dekko Services, LLC
Dept 01.073
Dock 108
6928N 400E
Kendallville, IN 46755
http://www.dekko.com





From:
Charles Wilt <charles.wilt@xxxxxxxxx>
To:
Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Date:
07/24/2009 09:26 AM
Subject:
Re: STRASPBAL on guested partitions
Sent by:
midrange-l-bounces@xxxxxxxxxxxx



Sue,

I'm curious, from a stand point of partition performance....

Does it matter if you have a single large virtual disk vs. multiple
smaller ones?

It would seem to me that the guested OS would benefit from having
access to multiple disks, given the OS's proclivity to RAID 0.  Unless
the host OS ended up putting all the smaller disks onto a smaller set
of physical disks?

Charles

On Thu, Jul 23, 2009 at 7:02 PM, Sue Baker<smbaker@xxxxxxxxxxxx> wrote:

 wrote on Tue, 30 Jun 2009 17:51:37 GMT:

Well, I found out, using IBM Director that if the first
one is over 90% used that it likes to alert people.

Rob, I'm sure this is because of the ASP threshold set in either
Director or in IBM i.

ASP balancing does work from a GBs or *CAPACITY perspective, but
none of the other ASPBAL options will do anything with virtual
disks.

--
Sue
Americas Technical Sales Support - Power Systems i
Rochester, MN
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