External volumes are located in an external storage system and are mapped as internal volumes. For details about Universal Volume Manager and external volumes, see the Universal Volume Manager User Guide for VSP One Block.
Consider the following when using external volumes with Compatible FlashCopy® V2:
- If an external volume is specified as a Compatible FlashCopy® V2 T-VOL, be careful about setting the time of path blockade, which is the time from when the external storage system is disconnected to when the path is blocked. If the time of path blockade watch set for the T-VOL is longer than the time of the MIH timer which is set for the S-VOL for the host side, MIH might occur on the S-VOL and the processing might end abnormally when the external storage system is powered off or when failures occur.
- To give higher priority to host I/O to the S-VOL than to host I/O to the T-VOL, set a smaller time value for the time of the path blockade watch for the T-VOL than the value set for the MIH timer for the S-VOL. By doing this, the Compatible FlashCopy® V2 relationship will be suspended when the T-VOL is blocked because of the path blockade watch, but the host I/O to the S-VOL will continue.
- To give higher priority to T-VOL host I/O than to S-VOL host I/O, use the default setting for the time of path blockade watch for the external volume to be used as the T-VOL.