Splitting ShadowImage pairs

ShadowImage User Guide

Version

9.8.5

Audience

anonymous

Part Number

MK-98RD9021-15

You must have Storage Administrator (Local Copy) role.
In CCI, use the pairsplit command.
If you split a pair when there are write I/Os to the P-VOL, only some of the write I/Os may be written to the S-VOL. To ensure that all write I/Os are written to the S-VOL, stop I/Os to the P-VOL before splitting the pair. You can maintain data consistency of the S-VOL (maintain the order in which data is written to the S-VOL) by using a consistency group pair-split to split a pair, or by stopping all I/Os to the P-VOL before splitting the pair.
P-VOL data and S-VOL data are synchronized when the pair status changes from COPY(SP)/COPY or PSUS(SP)/PSUS to PSUS. Because SI update copy is performed asynchronously, it takes some time before the pair status changes.
To ensure data consistency in the P-VOL and the S-VOL after a split, stop write I/Os from the host to the P-VOL in advance. By this method, you can keep the P-VOL from being updated during a split, and ensure data consistency between the P-VOL and the S-VOL.
The pair status must be one of the following:
- If you are splitting an existing pair, the pair status must be PAIR.
- If you are creating and then immediately splitting an L1 pair, the volumes are unpaired (SMPL).
- If you are splitting an L1 pair that has L2 pairs, see L1, L2 pair status and supported pair tasks.
- If you are splitting, or creating and immediately splitting, an L2 pair, the status of the L1 pair must be PSUS.
To split pairs quickly, stop host access to the P-VOL before splitting the pairs.
Check the I/O load to verify that it will not affect host server performance.
For more information about checking I/O performance, see the System Administrator Guide.
If you split a pair during initial copy, the initial copy operation is canceled, and it is performed again after the split. For initial copy, the maximum copying multiplicity (the number of jobs used for concurrent copy processing) for each pair is 24, but the number might change to 1 after the split. As a result, if you split a pair during initial copy, copy processing might take longer than splitting a pair after initial copy completes.
The copy processing to split a pair requires some time to check if the differential data exists even if there is no differential data. The amount of time to check the differential data takes longer as the volume capacity increases, and it might take 10 minutes or more for 256 TB.

In the Explorer pane, click Storage Systems, expand the storage system tree, and then click Replication > Local Replication.
In the Local Replication window, select the SI Pairs tab.
On the SI Pairs tab, select the pair you want to split, and then click Split Pairs.
In the Split Pairs window of the Split Pairs wizard, complete the following steps:
- For Split Type, select the split type.
  Values:
  
  - Quick Split (default): Splits the new pair, and then copies the data so that the S-VOL is immediately available for read and write I/O. The storage system copies the remaining differential data to the S-VOL in the background.
  
  - Steady Split: Copies the differential data to the S-VOL, and then splits the new pair.
  
  For more information about the methods you can use to split pairs, see Pair splitting methods.
- For Copy Pace, select the rate at which you want the storage system to copy data.
  Values:
  
  - Slower: Improved host server I/O performance but slower processing speed.
  
  - Medium (default): Average processing speed and host server I/O performance.
  
  - Faster: Faster processing speed but slower host server I/O performance.
  
  Note: The pace you select affects processing speed and host server I/O performance.
  For more information about performance, see Performance planning for ShadowImage.
Click Finish, and then confirm the settings.
Accept the default task name or enter a unique name.
You can enter up to 32 letters, numbers, and symbols, except the following:
\ / : , ; * ? " < > |
If you want to monitor the task after submitting it, select Go to tasks window for status.
Click Apply to submit the task.
The SI pair is split and the pair status changes from PSUS(SP)/PSUS or COPY(SP)/COPY to PSUS. The snapshot data is consistent with the P-VOL data and is ready to use in SI pair tasks.