Re: Virtual disks for an i partition

[Sue Baker <smbaker@xxxxxxxxxx>]

Pete, a bladecenter-s (BCS) is a little bit of a different critter than 
the servers Pete, Larry, and Rob work on.  That said, here are some 
answers to your questions.


On 2/11/2013 3:54 PM, Pete Helgren wrote:
> I seem to recall that the recommendation for VIOS installation use two
> mirrored physical disks but now I am not so sure that is necessary if
> the 6  320 GB drives in the SAS cage were one volume and then two
> smaller virtual disk were carved out for VIOS.  Is my assumption about
> physical disks for VIOS incorrect?

Yes, VIOS should protect the disk used for rootvg.  However, if my 
memory serves me, you will use the disk on the blade for rootvg, not the 
disks in the BCS, so protecting it becomes problematic because there's 
only 1.  (My memory may be failing me on that point!  There may be 2 
disks on the blade, in which case, you would run mirrorios to get disk 
level mirroring.)

> If I understand Rob and the good Doctor correctly, I should carve out at
> least 6 virtual disks for IBM i?  Then in IBM i I also create a RAID
> array from those 6 disks (or is that redundant?)

IBM i cannot "turn on RAID" protection for the drives in a BCS.  You 
will either create parity sets from VIOS or you'll give the drives 
straight to IBM i and use mirroring to protect them.

Regardless, if you need good save/restore performance, you certainly 
want to have at least 6 "disks".  If save/restore isn't critical, you 
can get by with 2-5 "disks".  My testing showed that getting to 6 drives 
cut average save/restore times in half when compared to any 
configuration of fewer disks.

> I guess I never fully virtualized my thinking:  The configuration of IBM
> i on VIOS should mimic a physical configuration. Yes?

With the BCS hardware, you can have it mimic a physical configuration, 
but it doesn't have to.