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Re: Ask the Expert: Performance Calculations on Clariion/VNX

if the pool can handle 37600 IOps, it's the total of read AND write, so if you're doing 10000 read IOps, that leaves 27600 for writes.

If these 27600 are 100% RAID5, then that means it's 27600/4 host IOps. If it's 100% on RAID6, that's 27600/6 host IOps. If it's  50/50 as seen by the storage, so 50% to RAID5 and 50% to RAID6, 27600/2 = 13800 for RAID5 and 13800 for RAID6. That means 13800/4 = 3450 host IOps to RAID5 storage and 13800/6 = 2300 host IOps to RAID6 storage.

So summarized:

10000 read IOps

3450 write IOps to RAID5

2300 write IOps to RAID6

10000 + 3450x4 + 2300x6 = 37600.

BUT: since you don't know where every 256 MiB block resides of a random LUN in your pool, you still can hit slow storage when you're in need of faster storage. And that's where FAST Cache comes in: it absorbes writes to flash instead of SAS or NL-SAS and it places blocks in cache when accessed more than 3 times (I think it was 3).

So your pool can do 37600 IOps, but that doesn't mean every block in every LUN has that performance. It's the total of the pool and assuming the hot spots never move, these are placed in flash and the almost dead data resides in NL-SAS. If you see a lot of data movement every day, that might indicate that your flash or SAS tier is too small.

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