Data replication between the and the is managed by the , which is transparent to machines and software applications. When the of the primary logical drive receives a write request from a host, the controller first logs information about the write to a . The controller then writes the data to the primary logical drive. Next, the controller initiates a operation to copy the modified data blocks to the secondary logical drive at the secondary .
The type of that you chose when you created the determines when the I/O completion indication is sent to the host software application, which signals that the data has successfully been copied to the secondary storage subsystem.
Choose one of these write modes shown in the table.
Write Mode | Description |
---|---|
Synchronous (recommended) |
This write mode offers the best chance of full data recovery from the secondary storage subsystem in the event of a disaster, at the expense of host I/O performance. When you select this write mode, any host write requests are written to the primary logical drive and then copied to the secondary logical drive. The controller sends an I/O completion indication to the host system after the copy has been successfully completed. This write mode is selected by default and is the recommended write mode. |
Asynchronous |
This write mode offers faster host I/O performance, but it does not guarantee that the copy has been successfully completed before processing the next write request. When you select this write mode, host write requests are written to the primary logical drive. The controller sends an I/O completion indication back to the host system before the data has been successfully copied to the secondary storage subsystem. |