Re: Use mixed sizes drives in the same Raid string

[DrFranken <midrange@xxxxxxxxxxxx>]

Careful on the disk speed. Most 520 class machines (Marco's included)  
are using FC #4326's which are 15K RPM vs the older FC #4319's which are 
the 10K RPM units. All of the FC #432x drives are the same speed - 15K 
RPM and interface throughput as well.  I would disagree with the 
assertion that upgrading from 10K RPM to 15K RPM is a  better 
performance boost that adding arms and RAID cards. I can't say that in 
some instances it could help more but IBM i handles up to 2000 arms per 
partition and does so incredibly well. Adding arms and RAID cards (with 
caches) and buses and loops will always help an I/O intensive installation.

You will certainly get better performance adding a FC #0595 or FC #5095 
due to the increased arm count and additional RAID card than updating 
the drives in the system unit.

As to power and cooling those are absolutely valid points. A 5095/0595 
drawer with 8 drives in it is going to pull 200 to 250 watts and toss 
out 800 to 850 BTU. Actual power consumed will be roughly 2.2 times that 
much once you consider cooling load and UPS efficiency factors, so as 
much as 550 watts.  Of course this is 24 hours a day as well so do the 
math at your power rate to compute the cost. And then there is 
maintenance as you will need to cover this unit that way as well.

Unload/Reload works done it uncountable times. So long as you're on V5R4 
or newer you can save your spooled files as well.

Certainly your call as you consider the factors.

   - DrFranken

On 4/15/2010 9:15 AM, rob@xxxxxxxxx wrote:
> It's not just the saving of a few euros.  It's also
> - Reduction in power consumption.  That side car is going to suck energy
> and require additional power feed(s).
> - Increase in speed.  The 70GB drives are 15K speed versus 10K speed.  If
> you're bad at math that's a 50% increase in speed.  Extremely significant!
>   This speed will outweigh the additional disk arms you will be getting.
> Been there, done that.
> - Affect on cooling.  You add a sidecar, you add BTU's.
>
> You are running an i.  Therefore you can have faith in your backups
> (providing you follow the steps).  Hundreds of us have done
> unloads/reloads.
>
>
> Rob Berendt
>