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413
January 16th, 2013 07:00
Where does the parity calculation happen. At the SPs?
I have a CX4 with service processors that are too overloaded. I'm wondering if RAID5 parity calculations are done here. I have a fair amount of available disk but not enough horse power in the SP's to service them. I'm wondering if going to a RAID1 or RAID10 for our write intensive apps might lessen the load on the SP's. It would certainly lessen the backend IOPS. All thoughts greatly appreciated.
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SushantGulati
55 Posts
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January 16th, 2013 07:00
You are right. Switching to a mirror RAID configuration would definitely ease off the load of parity calculations from the Service Processors.
Having said that can you please enlighten us about the SP configuration or CX4 model? How are you determining that the parity calculations are causing heavy load on SPs. Also, CX4 doesnt seem to be an underpowered system, so parity calculations should not be a problem. Can you also provide some information about you IO workload? (Total IOPS, Read to write ratio, etc.)
revmanii
3 Posts
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January 16th, 2013 08:00
Thank you for your reply. The array is an NS-480 with two SPs. I’m not saying that I think parity calcs are causing the high cpu on the SP’s, but I was considering taking our VDI work load which is about 50/50 read/write and moving it to RAID10 for better performance and I was wondering if this would also have the side benefit of putting a little less stress on our SPs, both from parity calcs and backend IOPS needed. They are running around 75-80 utilization on average.
SushantGulati
55 Posts
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January 16th, 2013 09:00
Thanks
Yes definitely as you say you have a 50:50 R/W load then its advisable to move to R10. Parity calculations put load on Service processors and the RAID penalty of R5 for a 50:50 RW IO workload would be substantial. You should see clear improvement in performance once you move to R10. I hope to get some more inputs on this discussion from others as well.
kelleg
4.5K Posts
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January 16th, 2013 13:00
Sushant is correct - with random Writes, there will be a heavy write parity penalty for R5. If you have licensed Analyzer installed on the array you would collect an Archive and review the level of IOPS or Bandwidth going to the disks. The Help provides a lot of information about using Analyzer and how to collect the archives. On PowerLink you can look for Support Solution emc218259 - this is a master article that lists all the other articles about Analyzer and it's use.
glen
AnkitMehta
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January 16th, 2013 21:00
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