How ShadowImage works

A pair is created when you:

• Select a volume that you want to duplicate. This becomes the primary volume (P-VOL).

• Identify another volume to contain the copy. This becomes the secondary volume (S-VOL).

• Associate the P-VOL and S-VOLs.

• Perform the initial copy.

During the initial copy, the P-VOL remains available for read/write. After the copy is completed, subsequent write operations to the P-VOL are regularly duplicated to the S-VOL.

The P-VOL and S-VOLs remain paired until they are split. The P-VOL for a split pair continues to be updated but data in the S-VOL remains as it was at the time of the split. The S-VOL contains a mirror image of the original volume at that point in time.

• S-VOL data is consistent and usable. It is available for read/write access by secondary host applications.

• Changes to the P-VOL and S-VOL(s) are managed by differential bitmaps.

• You can pair the volumes again by resynchronizing the update data from P-VOL-to-S-VOL, or from S-VOL-to-P-VOL, as circumstance dictates.