If you detect an error on the path that is currently being used, you can continue to use the system by having the status of that path automatically changed to offline, and then automatically have the system switch over to another online path. This functionality is called automatic failover. Automatic failovers can be used for the following levels of errors:
- Error
A high-risk error, which can be avoided by performing a failover or some other countermeasure.
For details on error levels, see Filtering of error information.
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.
If the storage system is supported by HDLM, usually all paths are owner paths. As a result, all of the paths accessing the same LU can be possible switching destinations. For example, in Figure 1, the LU is accessed using only the one path (A). However, after that path is placed offline, the switching destination can come from any of the other three paths (B, C, or D).
When non-owner paths exist, HDLM will select the path to be used next from among the various paths that access the same LU, starting with the owner paths, and then the non-owner paths. For example, in Figure 1, assume that the paths on the CHA0 side are owner paths and the paths on the CHA1 side are non-owner paths, and that 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.
- Note
Non-owner paths exist in the following cases:
When a global-active device is being used, and the non-preferred path option is set