Re: What is a disk arm? -- MIDRANGE-L

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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

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