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March 11th, 2015 09:00
VMAX BE and Host reads writes
In my environment, I have a VMAX10K -2 Engine equipped with 3 thin pools from 3 Tiers comprising of 64 EFDs, 240 15k FC and 60 SATA drives. All storage groups are bound to FC thin pool. While going through HOST IOs on Unisphere Performance Dashboard, I noticed a sharp climb of BE reads(30,000) and BE writes (35,000). It was the instance of 40,000 Host Reads and only 6,000 Host Writes (Very less in comparison to BE writes). My question is - how can we interrelate the BE read/write to Host read/write? Would be interesting to know how the HOST IOPS are distributed among the Disk Tiers.
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RRR
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March 15th, 2015 07:00
Hello iDIG IT,
you might consider moving this discussion to the Symmetrix forum, where more people will notice the question. You can find the Symm forumon ECN here: Symmetrix Support Forum
RRR
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March 15th, 2015 07:00
I can't directly explain the numbers you're giving us, but if your tiers are in RAID5, every host write I/O will do 2 reads and 2 writes on the BE. So suppose your host does 6k IOps in RAID5, I'd expect to see 12,000 reads per second and 12,000 writes per second. Why the reads? Since parity has te be recalculated, it will read the data that's going to be overwritten as well as the parity in that stripe (that's 2 reads so far), then the write of the new data as well as the new parity (and that's 2 writes). So for 1 host write IO, you'll get 4 back-end I/Os. For a host read I/O, there's only 1 BE I/O.
In RAID1 (10) every host write is just 2 BE I/Os (mirroring)
shiko1
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March 15th, 2015 17:00
I shall have mentioned that EFD is configured to RAID 5 (3+1), FC to R1 Mirroring and SATA to RAID6 (6+2). It is understandable that 1 Host write ends up with 2 BE I/Os in R1, 4 BE I/Os in R5 and 6 BE I/Os in R6. Hope to get more feedback.
RRR
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March 19th, 2015 04:00
Let's see what happens. I guess more people will see your post here.