HP Hitachi Dynamic Link Manager Software User Manual

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2. HDLM Functions

(1) When Using the Thunder 9500V Series, or Hitachi AMS/WMS Series

When HDLM performs load balancing, it differentiates between load balancing among

owner paths and among non-owner paths. An owner path is a path that passes through

the owner controller for a target LU. When you set up an LU, you have to specify

which CHA to be used as the owner controller for the LU. Because different LUs might

have different owner controllers, different LUs might also have different owner paths.

A non-owner path is a path that passes through a CHA other than the owner controller.

This type of CHA is also known as a non-owner controller. An owner path is usually

used in preference to a non-owner path. In order to prevent system performance from

slowing down, HDLM does not perform load balancing between owner paths and

non-owner paths. If failures occur across some of the owner paths, load balancing will

be performed among the remaining, usable owner paths. It is only when absolutely no

owner paths are available, that load balancing is then performed among the non-owner

paths.
For the example in Figure 2-7: Overview of load balancing, suppose that in the

owner controller of LU0 is CHA0. When the LU is accessed, the load is balanced

between the two paths A and B, which are both owner paths. When one of the paths

(A) cannot be used, then the LU is accessed from the only other owner path (B). When

the physical paths (A) and (B) cannot be used, the load is balanced between the

physical paths (C) and (D) (that is, between non-owner paths).