Dell Acceleration Appliances for Databases - Manual (Page 39)

ABOUT MULTIPATHING
Multipath I/O (MPIO) establishes multiple routes and connections to a storage array, using redundant
physical paths (adapters, cables, switches). That way, when a component fails, an alternate I/O path
is used. Multipathing provides redundancy of I/O paths and can improve overall system performance.
Before multipathing is installed, you see one drive for each path setup (so with two paths, you see
two drives). After multipath installation, you will see a single drive for all paths of the same drive. The
drive Properties dialog, available by right-clicking on the drive in the Disk Management tool, now has
a multipath tab, where the load-balance policy is set.
If you are using Fibre Channel, make sure you have the latest HBA driver installed before
configuring multipathing.
LOAD-BALANCE POLICIES FOR MPIO
Below are some basic load-balance policies typically used with multipathing:
• Round-robin, subsets: Standby paths are used only if all primary paths fail.
For Windows MPIO, the “round-robin with subsets” method is required for HA
configurations; for Windows standalone configurations, round-robin or dynamic least queue
depth methods may be used, with the latter generally preferred.
• Failover: No balancing; standby paths are used.
• Failback: I/O is rerouted to preferred path when available.
• Round-robin: All available paths are used for balanced I/O.
• Dynamic least queue depth: I/O to path with fewest outstanding requests (in Linux, this is
“queue-length”). This enables multipathing to compensate for an unbalanced load on the
fabric. This may be advantageous for standalone configurations.
• Weighted path: Paths are assigned priority weights.
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