Hitachi XP P9500 User Manual page 46

2. HDLM Functions
that uses a CHA other than the owner controller (a non-owner controller). Paths used
for load balancing are selected from owner paths first, then non-owner paths. To
prevent performance in the entire system from deteriorating, HDLM does not perform
load balancing between owner paths and non-owner paths. When some owner paths
cannot be used due to a problem such as a failure, load balancing is performed among
the remaining usable owner paths. When all owner paths cannot be used, load
balancing is performed among the non-owner paths.
For the example in Figure 2-9: 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
both of the owner paths (A and B) cannot be used, the load is then balanced between
two other, non-owner paths (C and D).
Figure 2-9: Overview of Load Balancing
(2) When Using the Lightning 9900 Series, Lightning 9900V Series, Hitachi USP,
Universal Storage Platform V/VM, Virtual Storage Platform, Hitachi AMS2000
Series, or Hitachi SMS
All online paths are owner paths. Thus, for the example in Figure 2-8: Flow of I/O
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