Re: What is a disk arm?

[Buck Calabro <kc2hiz@xxxxxxxxx>]

On 6/13/2013 4:31 PM, Roberto José Etcheverry Romero wrote:
> Can you do a test? Try to do a Pwrdwnsys *immed without ending anything
> beforehand (if such a thing is safe for the system to do) and time it. It's
> not the Worst Case, but it should be a good starting point. I doubt very
> much that with 20 arms on a p7 the pwrdwnsys takes that long...
> And yes, 1 disk = 1 arm, but beware of virtualization and LUNs and the
> like. if those 20 disks are virtual devices on a 400 disk storage, then
> it's gonna be faster, if those 20 disks are on a 4 disk raid5, grab a
> papyrus, it'll be faster to transcribe the contents...

Thanks Roberto.  Your thoughts on virtualisation and RAID are a good
reminder of things to take into account.  I think I will send reader
feedback to IBM on those points.

A 'normal' PWRDWNSYS takes between 3 and 7 minutes.  I need to balance
'normal' vs the risk of the UPS cutting out before the machine has saved
all of the 'worst case' main store to disk.  No wonder QUPSDLYTIM *CALC
is only 200 seconds.
  --buck