Ensure you are familiar with the homogeneous queue depth
calculation.
The homogeneous queues must meet one of the following
statements:
- The queued commands are shared among all paths rather than providing
servers with additional resources.
- The virtual disks (VDisks) are distributed evenly among the input/output
(I/O) groups in the cluster.
You can set the queue depth for each VDisk on the servers using
the following calculation:
q = ((n ×7000) / (v×p×c))
where:
- q is the queue depth per device path
- n is the number of nodes in the cluster
- v is the number of VDisks configured in the cluster
- p is the number of paths per VDisk per host. A path is
a route from a server fibre-channel port to a SAN Volume Controller fibre-channel
port that provides the server access to the VDisk.
- c is the number of hosts that can concurrently access each
VDisk. Very few applications support concurrent access from multiple
hosts to a single VDisk. This number typically is 1.
Example
Consider the following example:
- An eight-node SAN Volume Controller cluster (n = 8)
- 4096 VDisks (v = 4096)
- One server with access to each VDisk (c = 1)
- Each host has four paths to each VDisk (p = 4)
The calculation is ((8×7 000)/(4096×4×1)) = 4.
The
queue depth in the operating systems must be set to four concurrent
commands per path.