You must set the homogeneous queue depth to a calculated value in Fibre
Channel hosts.
The homogeneous queues must meet the following criteria:
- The queued commands must be shared among all paths rather than providing servers with more
resources.
- The volumes must be distributed evenly among the I/O groups in the clustered
system.
Set the queue depth for each volume on the servers by using the following calculation:
- q = ((n * 7000) / (v * p * c))
Where
- q = the queue depth per device path
- n = the number of nodes in the system
- v = the number of volumes that are configured in the system.
- p = the number of paths per volume per
host. A path is a route from a server Fibre Channel port to a
system Fibre Channel port
that provides the server access to the volume.
- c = the number of hosts that can concurrently access each volume. Few
applications support concurrent access from multiple hosts to a single volume. This number typically
is 1.
Consider the following example:
- An eight-node
system (n = 8)
- 4096 volumes (v = 4096)
- One server with access to each volume (c = 1)
- Each host has four paths to each volume (p = 4).
The calculation is rounded up to the next complete digit:
- ((8 * 7000) / (4096 * 4 * 1)) = 4
The queue depth in the operating systems must be set to
four concurrent commands per path.