Homogeneous queue depth calculation in Fibre Channel hosts

You must set the homogeneous queue depth to a calculated value in Fibre Channel hosts.

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 or a server iSCSI port to a system iSCSI 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:
  • A two-node system (n = 2)
  • 1024 volumes (v = 1024)
  • 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:
  • ((2 * 7000) / (1024 * 4 * 1)) = 4

The queue depth in the operating systems must be set to four concurrent commands per path.