Re: Why host? Was: IBM i vs VIOS for Host Partition

[Jim Oberholtzer <midrangel@xxxxxxxxxxxxxxxxx>]

Rob,

The additional power of another disk controller will not mitigate the 
queuing that goes on inside IBM i for I/O, therefore unless you have six 
arms or more, you are reducing the available performance of I/O.   
(which might be OK in some situations where I/O is not a significant 
factor in the application, but it will affect backup/restore)  What 
you'll have is a disk controller that's way under utilized.  Put another 
way, you'll only be getting about 2% or 3% of your investment in the 
card back.

In the case you cite, your better off creating a series of smaller 
virtual disk units so you wind up with as many as you can for the space 
you need.

VIO Server really does not change the equation at all, it's just another 
method of virtualization.

Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects


On 4/18/2013 6:17 AM, rob@xxxxxxxxx wrote:
> We host some guest partitions because it reduces the cost of hardware. You
> don't have to have a separate disk controller for each lpar.  Part of me
> has to wonder if 12 disk arms shared between the host and two guests would
> be a better performer then 3 dedicated lpars with only 4 arms each.  Ok, a
> separate disk controller for each could blow that away though.
>
> I consider this a good enough reason to host.  Are there others?  Well,
> perhaps VIOS san support?
>
> Let's take it to the extreme.  Now we have a very large guest, over a
> couple of TB.  We did it this way because we wanted to do it "now" and
> couldn't add another disk controller.  The boss is saying when we get our
> new hardware (which I think will be postponed quite some time due to the
> business numbers I saw yesterday), that we will make that a dedicated
> lpar.
>
>
> Rob Berendt
> -- IBM Certified System Administrator - IBM i 6.1 Group Dekko Dept 
> 1600 Mail to: 2505 Dekko Drive Garrett, IN 46738 Ship to: Dock 108 
> 6928N 400E Kendallville, IN 46755 http://www.dekko.com
> --