What is a write consistency group?

 is a configuration option available for any  or  participating in a  that have been configured to use the  and to preserve write order.

When Asynchronous Write mode is selected, any write requests to the primary virtual disk are completed by the  without waiting for an I/O completion indication from the secondary, remote  that the data was successfully copied to the secondary virtual disk.

As result of selecting this , writes requests are not guaranteed to be completed in the same order on the secondary virtual disk as they are on the primary virtual disk. If the order of write requests is not retained, data on the secondary virtual disk might become inconsistent with the data on the primary virtual disk and could jeopardize any attempt to recover data if a disaster occurs on the primary storage array.

When multiple Remote Virtual Disk Mirrors exist on a single storage array have been configured to use Asynchronous Write mode and to preserve consistent write order, they are considered to be an interdependent group, known as a . The data on the secondary, remote storage array cannot be considered fully synchronized until all Remote Virtual Disk Mirrors in the write consistency group are synchronized.

If one Remote Virtual Disk Mirror in a write consistency group becomes Unsynchronized, all of the Remote Virtual Disk Mirrors in the write consistency group will become Unsynchronized, and any write activity to the remote, secondary storage arrays is prevented to protect the consistency of the remote data set.

Note: Mirrored pairs that have been configured with the  option remain in a  until you intervene by issuing a Resume command. Mirrored pairs configured with the  option will automatically resynchronize and recommence write-consistent I/O operation.

Example:

On a campus site, Remote Virtual Disk Mirroring has been configured between two storage arrays. At the primary site, the primary storage array has three Remote Virtual Disk Mirrors (RVM-A, RVM-B, and RVM-C), with each mirrored pair configured to copy data to the secondary storage array, at a remote secondary site.

All three Remote Virtual Disk Mirrors have been configured to use the Asynchronous Write mode and to preserve write order. If the mirrored pair RVM-A becomes Unsynchronized due to a link interruption, the RAID controller module will automatically transition RVM-B and RVM-C into an Unsynchronized state until communication can be resumed.