Nonhomogeneous queue depth calculation in iSER hosts
After you understand certain criteria for nonhomogeneous queues, you can calculate their queue depth in iSER hosts.
Nonhomogeneous queues must meet one of the following criteria:
- One or more servers must be allocated more resources so that they can queue more commands.
- Volumes must not be distributed evenly among the I/O groups in the clustered system.
For each volume, consider each server to which that volume has a mapping in an I/O group. This mapping results in a set of server/volume pairs. If the sum of the server and volume queue depth for all of the pairs is less than 4000, the server does not experience problems due to a full queue.
Example
Consider a situation with 20 host servers and 2 I/O groups, iogrp0 and
iogrp1. In iogrp0, 20 volumes are mapped to 20 host servers. In
iogrp1, 40 volumes are mapped to the same 20 host servers. Using the formula that
is described in Homogeneous queue depth calculation in iSER hosts, the following values
are derived:
- For
iogrp0:v = 20c = 20q = (4000/20 * 20) * 0.75 = 7(considering the lower boundary limit)
The total server-to-volume mapping is 400 (20 times 20), and queue depth for each volume is seven. Therefore, the sum of the queue depths for all mappings is 2800 (400 times 7). Because this amount is less than 4000, problems of full queues do not occur.
- For
iogrp1:v = 40c = 20q = (4000/40 * 20)) * 0.75 = 3(considering the lower boundary limit)
The total server-to-volume mapping is 800 (40 times 20), and queue depth for each volume is three. Therefore, the sum of the queue depths for all mappings is 2400 (800 times 3). Because this amount is less than 4000, problems of full queues do not occur.