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Mapping volumes to an ESXi server
29 Dell EMC SC Series: Best Practices with VMware vSphere | 2060-M-BP-V
6.9.1 Round robin policy for standard volumes
The round robin path selection policy uses automatic path selection and load balancing to rotate I/O through
all paths. Round robin load balancing does not aggregate the storage link bandwidth. It merely distributes the
load for the datastore volume in bursts evenly and sequentially across paths in an alternating fashion.
Using round robin reduces the management headaches of manually balancing the storage load across all
storage paths as with a fixed policy. However, there are certain situations where using round robin does not
make sense. For instance, it is not considered a best practice to enable round robin between an iSCSI path
and Fibre Channel path. It is also not best practice to balance the load between an 8 Gb FC and a 16 Gb FC
path. With round robin, care must be taken to ensure all the paths included are identical in type, speed, and
have the same queue depth settings.
Here is an example of what happens during a path failure when using round robin:
1. Load is distributed evenly between HBA1 and HBA2
2. HBA1 loses connectivity; HBA2 will assume all I/O load
3. HBA1 resumes connectivity; load is distributed evenly again between both
Example of a datastore path selection policy set to round robin