Hitachi Dynamic Link Manager Software Users Guide for AIX (6.6) (T5208-96010, April 2011)

2. HDLM Functions
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For details on error levels, see 2.10.2 Filtering of error information.
When the Thunder 9500V series, or Hitachi AMS/WMS series is being used, HDLM
will select the path to be used next from among the various paths that access the same
LU, starting with owner paths, and then non-owner paths. For example, in
Figure 2-8: Path switching, the owner controller of an LU is CHA0, and access to the
LU is made via only one path (A). After that access path (A) is placed offline, the first
choice for the switching destination is the other path connected to CHA0 (B). If an
error also occurs on that path (B), then the next possibility for a path comes from one
of the two paths (C or D) connected to CHA1.
When the Lightning 9900V series, Hitachi USP, Universal Storage Platform V/VM,
Virtual Storage Platform, Hitachi AMS2000 series, or Hitachi SMS is being used, all
the paths are owner paths. This means all the paths accessing the same LU can be
possible switching destinations. For example, in Figure 2-8: Path switching, the LU
is accessed using only the path (A). After the access path is placed offline, the
switching destination is one of the paths (B), (C), and (D).
For details on the priority for determining which of the paths to the same LU is used
as the switching destination, see (2) Priority of Switching Destination Paths.