Re: Isolate Load Source Drive

Brian wrote on Tue, 07 Feb 2006 19:30:24 GMT:

> How can I permanently keep data from being stored on my load
> source drive? 
> 
> 

Brian, looking to answer only this question, you cannot do this.  
The load source unit stores much more than read-only IPL specific 
data and needs to fully participate in the system ASP.

Stepping back and looking at your configuration and performance 
concerns, I offer the following.

You didn't specify whether you have only 2 35G drives or 4 behind 
the base DASD controller.  You also didn't specify whether you 
have the 5709 or 5726 write cache plus RAID enabler daughter 
card.  If you don't have this card, you really should consider 
getting one to improve the performance of mirroring for your 
drives.  You can also look into the newer replacement features 
that were announced 1/31 that offer similar write cache, RAID 
capability, and performance.

I'm hoping that you have significantly more 145G drives than 35G 
drives and so the issue of mixed drive size performance isn't 
what comes into play here.  What we frequently see is that the 
larger drives get most of the IO workload and the smaller drives 
next to none because the disk requests "follow the GBs".  And in 
your circumstances, would be the desired behavior.

I've also seen some issues with customers that skip drive sizes, 
but without some pretty detailed analysis of your workload, I 
couldn't tell you if this will be an inherent issue in your 
environment or not.   

To get back to your questions, if you attempt to utilize 
something like independent or user ASPs to isolate load source, I 
think you'll quickly find that 2 or 4 drives just isn't enough to 
support all the disk requests that are needed even through 
there's more than enough gigabytes available.  If you attempt to 
run with the load source and its mirror in an *ENCALOC state, I'm 
pretty sure you'll end up with all sorts of odd errors from 
i5/OS.

HTH,