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VNX ALUA and vSphere 4.1 Path Selection Policy
Hello,
i am digging through a bunch of tech books ("Using EMC VNX Storage with VMware vSphere") and can't seem to locate a definitive answer on which path selection policy to use with NMP. When i presented LUNs from VNX to ESXi 4.1 (failover mode 4), they showed up VMW_PSP_FIXED_AP. When you look at paths, i only see one path for LUN listed as Active (I/O).
Here is my zoning:
HBA1 - SPA0, SPA1 , SPB2, SPB3
HBA2 - SPA2, SPA3, SPB0, SPB1
LUN is on SPA, so based on above zoning is there a reason to continue using the default policy or should i switch to Round Robin. When i switch to Round Robin i actually see 2 Active (I/O) paths on each HBA ..so i like that but is that the right thing to do?
I decided to test something by presenting another LUN from SPA and see what VMW_SPS_FIXED_AP woud do. Once again i only had one Active (I/O) path but this time it was on a different HBA. So i guess it's doing some kind of balancing but i would rather have 4 Active (I/O) paths to each LUN ?
Then there is emc232355 . What is the best setting ?
Thanks
RafaelNovo
92 Posts
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September 2nd, 2011 10:00
First of all: both FIXED and ROUND ROBIN are valid configs for VNX with ALUA.
So which to choose?
FIXED, as you mentioned, will only send the IO thru 1 path, so in order do balance, you must ensure that each ESX and each LUN has a preferred path and that those paths are all balanced.
ROUND ROBIN, will use all optmized paths automatically, so you don't have to worries about manually balancing the paths. But in a event of SP reboot, round robin will not failback the to the default SP what may cause some stress to the array, and you will have to do some work to manually solve this.
My suggestion: go for Powerpath/VE. Great software for a small price. If for some reason it's not possible, so RoundRobin will be my suggestion.
Regards,
Rafa