IBM DS6000 Series manual LSS13

Because of the time lag for Consistency Group operations, some volumes in some LSSs are in an extended long busy state and other volumes in the other LSSs are not.

In Figure 6-12,the volumes in LSS11 are in an extended long busy state, and the volumes in LSS12 and 13 are not. The 1st operation is not completed because of this extended long busy state, and the 2nd and 3rd operations are not completed, because the 1st operation has not been completed. In this case, 1st, 2nd, and 3rd updates are not included in the backup copy. Therefore, this case is consistent.

See Figure 6-13.In this case, the volumes in LSS12 are in an extended long busy state and the other volumes in LSS11 and 13 are not. The 1st write operation is completed because the volumes in LSS11 are not in an extended long busy state. The 2nd write operation is not completed because of an extended long busy state. The 3rd write operation is also not completed because the 2nd operation is not completed. In this case, the 1st update is included in the backup copy, and the 2nd and 3rd updates are not included. Therefore, this case is consistent.

Servers

LSS11

1st

Completed

LSS12

2nd

Wait

This write operation is completed because LSS11 is not in an extended long busy condition.

This write operation is not completed because LSS12 is in an extended long busy condition.

3rd

dependency for each write operation

LSS13

Wait

This write operation is not completed because 2nd write operation is not completed.

Figure 6-13 Consistency Group: Example 2

In all cases, if each write operation is dependent, Consistency Group operations can keep data consistent in the backup copy.

If each write operation is not dependent, the I/O sequence is not kept in the copy that is created by the Consistency Group operations. See Figure 6-14 on page 108. In this case, the three write operations are independent. If the volumes in LSS12 are in an extended long busy state and the other volumes in LSS11 and 13 are not, the 1st and 3rd operations are completed and the 2nd operation is not completed.

Chapter 6. Copy Services 107