specify the S-VOL, the data written to the S-VOL while the pair is
suspended will be copied to the P-VOL when the pair is resynchronized.
•
Pair resynchronization:
updates the S-VOL (or P-VOL) by copying the
differential data accumulated since the pair was suspended. The volume
that was not receiving update data while the pair was suspended is
resynchronized with the volume that was receiving update data. When
resynchronization completes, the host can read from and write directly to
the P-VOL or the S-VOL.
•
Pair deletion:
deletes the pair relationship between the P-VOL and the
S-VOL. The data in each volume is not affected. When you delete a pair,
you can specify the volume (P-VOL or S-VOL) that will receive update
data from the host after the pair is deleted. The virtual LDEV ID of the
unspecified volume is deleted, and the GAD reservation attribute is set for
the specified volume.
The following table specifies the required conditions for the volume that
will continue to receive update data from the host after pair deletion.
Volume to receive I/O after pair
deletion
Required conditions
P-VOL
•
Pair status: PSUS or PSUE
•
I/O mode: Local
S-VOL
•
Pair status: SSWS
•
I/O mode: Local
Initial copy and differential copy
There are two types of GAD copy operations that synchronize the data on the
P-VOL and S-VOL of a pair:
•
Initial copy:
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 executed
when the GAD status changes from Simplex to Mirrored.
•
Differential copy:
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.
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Overview of global-active device
Hitachi Virtual Storage Platform G1000 Global-Active Device User Guide
Summary of Contents for G1000
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