Splitting pairs

You can split a pair, which suspends data copying to the S-VOL.

When a pair is split:

• I/O writes from the host continue to the P-VOL, but stop to the S-VOL.

• Any current update copy operation completes to the S-VOL, ensuring data consistency to the point of the split operation.

• Pair status changes to PSUS.

• The primary system records the updated tracks to the P-VOL that occur after the split as differential data. This data is copied to the S-VOL when the pair is resynchronized.

• You can set an option to block updates to the P-VOL while the pair is split. This results in the P-VOL and S-VOL staying synchronized.

• Another option is to enable system write to the S-VOL from a host. The secondary system records the updated tracks as differential bitmaps. When the pair is resynchronized, the secondary system sends the differential bitmaps to the primary system, which merges all differential bitmaps to determine which tracks are out-of-sync.

Prerequisite information

• Pair status must be COPY or PAIR.

To split one or more pairs

1. In Hitachi Command Suite:

1. On the Resources tab, expand the Storage Systems tree, right-click the target storage system and click Remote Replication.

In Device Manager - Storage Navigator

1. Click Storage Systems, and then expand the Storage Systems tree.

2. In the Storage Systems tree, click Replication > Remote Replication.

2. In the Remote Replication window, click the TC Pairs tab, select the pair to be split then click Split Pairs.

3. In the Split Pairs window, ensure that the pair to be split appears in the Selected Pairs table.

4. For Secondary Volume Write, specify whether the host can write to the S-VOL while the pair is split.

• Enable. Accepts host writes to the S-VOL. Note the following:

- If you plan to resynchronize the pair after the S-VOL has been written to while split, you must select Depend on Primary Volume Fence Level for the Primary Volume Write option, below. This ensures that P-VOL and S-VOL bitmaps are merged when the pair is resynchronized.

- If you specify Enable for this option, and also need the P-VOL to continue accepting host I/O, make sure to select Depend on Primary Volume Fence Level for Primary Volume Write.

Enable is only available when performing the split operation from the pair's primary storage system.

• Disable (default), to cause host input to be rejected by the S-VOL while the pair is split.

5. For Primary Volume Write, specify whether writing to the P-VOL is enabled while the pair is split.

• Depend on Primary Volume Fence Level: Writing to the P-VOL is based on fence level specified during the Create Pairs operation. This is the default.

• Disable: Write I/Os to the P-VOL are rejected regardless of the fence level. Select this option to maintain synchronization of the P-VOL and S-VOL. Do not select this option if the P-VOL is necessary for host system operations.

Disable is only available when performing the split operation from the pair's primary storage system.

6. Click Finish.

7. In the Confirm window, review the settings and enter a task name in the Task Name box.

8. Click Apply to save your settings in the system.

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