Splitting mirrors

When you split a mirror, all of the pairs in the mirror are split, and copy operations of data from the master journal to the restore journal stop. To split a mirror, you must place the mirror in Active status. When mirror splitting is completed, the mirror status becomes Stopped.

Updated data is not reflected to the S-VOL while the pair is split, but only later when the pair is resynchronized. To resynchronize all of the pairs in the mirror, resynchronize the mirror itself.

You can select whether to enable the S-VOL write operation in the Secondary Volume Write option when you split a mirror. If the Secondary Volume Write option is enabled, the host can write data to the S-VOL while the pair is split.

You can also split a mirror after synchronizing the P-VOL and S-VOL. In that case, select Flush in Split Mode. This allows you to reflect the updated data to the S-VOL when the pair is split. When the secondary system accepts the pair split, all the journal data that has been held for the pair is written to the S-VOL. If no journal data (update data) comes to the pair for a fixed period of time, the pair status changes to PSUS. When all pairs in the journal are placed in the PSUS status, volume copying is complete, and the mirror status becomes Stopped.

To create a complete copy of the data volumes in the mirror, you need to stop I/O operations from the host. Creating an instantaneous copy-on-demand, and the copy created in this way, is called a "point-in-time copy".