Disk Arrays
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will changing settings "prefetch" and "array mode" help?

Sviatoslav Rimdenok
Occasional Advisor

will changing settings "prefetch" and "array mode" help?

Hello All!

we have got HP VA7400 array running HP18 firmware. It is occupied with 15x72GB disks.
We have problem with performance - I know that adding more disks (i.e. adding disk enclosure) helps, but we don't have such possibility.
Arrays operates in AutoRAID mode - I got some data from armperf and imported them into exceel sheet. Looks like only 10-15% of data are stored as RAID1+0.
I also noticed that during the times we had bad perfomance (data processing) - I could see high values of Forced Unit Access values (taken from armperf).
I checked documentation and looks like our array is working in "secure mode" :
Simplified Resiliency Setting:________Secure (High Recoverability)
Performance Goal Configuration:_______High Recoverability (Secure)

Could you please tell me if changing to "normal mode" will help improve perfomance? Do I need to reset array to implement that setting or can it be done on-the-fly?

I have also another setting which could be tuned - "enable prefetch". Currently it is disabled. But HP doc says that it could make perfomance worse sometimes. I would like to play with that setting as well - do I need to reset array to implement that setting?

By the way : what is a reason to run array in "secure mode"? As I understood there are batteries - so NVRAM will be written to disks anyway in case of power failure. Do I understand it correctly?

thank you in advance!

Slava R.