Raid Calculations and SP Utilization

Question

I know SP's handle many tasks that add to their utlization like Raid creation, lun creation management and such. Does anyone know how much of SP utlization is driven by Raid Calculations? I currently assume it is the majority of any SP's Utilization. I know the write penalties for Raid 10, 5 and 6 and as you go between these different Raid types the write penalty climbs. So higher write penalty translates into more work on the SP's is that correct?

Thanks,

Mike

hpeskens · Answer

Dont know how much SP utilization is used by RAID, probably depends....

The raid overhead is the following (I assume that all writes will be random, in case of sequential writes, the CLARiiON will write a full stripe and you do not have the RAID overhead):

RAID 1(/0) - two writes to the 2 components, so 2 IOs for one write IO

RAID 5 - two reads (of the data and parity), XOR calculation of the differences between old - new data, and write of data and parity, so 4 IO for 1 write IO and the XOR calculation load on the SP.

RAID 6 - three reads (of the data and 2x parity), XOR calculation of the differences between old - new data, and write of data and parity so 6 IO for 1 write IO and the XOR calculation load on the SP.

So you have 2 things that increase load on the SP, more IOs, and the XOR calculations.

Also replication (either local or remote) will also use SP utilisation.

RRR · Answer

Indeed. It's not the drives that do the calculations, so the SPs will get busy doing the calculations

Christoffer3 · Answer

Hi there,

Not entirely what you wanted, but if you look through the following whitepaper:

H4153-the-influence-of-priorities-on-lun-mgmt-optns-wp.pdf

You'll find some graphs and info regarding SP cpu utilization when it comes to LUN management tasks (migration/rebuilds and so).

Might be an interesting read for you.

Best regards

Christoffer

CLARiiON

Raid Calculations and SP Utilization

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