Initial copy and differential copy

Ops Center High Availability User Guide

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There are two types of GAD copy operations that synchronize the data on the P-VOL and S-VOL of a pair, initial copy and differential copy.

For an initial copy operation, all data in the P-VOL is copied to the S-VOL, which ensures that the data in the two volumes is consistent. The initial copy is run when the GAD status changes from Simplex to Mirrored.

For a differential copy operation, only the differential data between the P-VOL and the S-VOL is copied. Differential copy is used when the GAD status changes from Suspended to Mirrored.

When a GAD pair is suspended, the storage systems record the update locations and manage the differential data. The following figure shows the differential copy operation for a pair in which the P-VOL received server I/O while the pair was suspended. If the S-VOL receives server I/O while a pair is suspended, the differential data is copied from the S-VOL to the P-VOL.