ESXi Server has one HBA with dual port and configured with zoning and path selection is set to round robin.
How many path (s) will be used by ESXi server to access VMFS?
A.
2
B.
3
C.
1
D.
4
Explanation:
Round Robin alternates paths continuosly – only really utilizing one path. Round Robins USE- CASE is usually when working with active/active SAN Controllers.
For Round Robin path selection to be effective, active active paths are required. Although IO operation initiation will be alternated between paths, with any heavier IOP loading there will be occasion for the ESXi server to be using both paths simultaneously. Neither the host nor the HBA require the operation on one port to complete before the IO operation on the other port commences. While a single IO operation always uses one port or the other, the ESXi server uses both ports — sometimes consecutively, sometimes simultaneously. IMO the answer should be A. 2.
Further to the above. The default RR IOPS before changing paths is 1000. This could be changed.
Here is a test of the improved performance a change to 1 achieves. http://jpaul.me/?p=2492
Also HP recommends this as a best practice on page 28.
http://h20195.www2.hp.com/V2/GetPDF.aspx/4AA1-2185ENW.pdf
The above is for iSCSI. It may be different for FC.
Here is an EMC document testing Round Robin change path values from 1 to 1000 with Fibre Channel.
http://www.emc.com/collateral/hardware/white-papers/h8119-tuning-vmware-symmetrix-wp.pdf
They found that some workloads benefit from a value of 1 while others do not. The recommendations are on page 33.