Read and Write Operations

After the volume mirror is created and the two drives on the primary and secondary servers are synchronized, the following events occur:

• The system locks out all user access to the target volume; reads and writes are not allowed to the target volume. The source volume is accessible for both reads and writes.

• Both mirrored and non-mirrored volume read operations arriving at the driver on the primary server are passed on and allowed to complete normally without intervention. Reads of a mirrored volume on the secondary system are not allowed, i.e., the secondary has not assumed the role of a failed primary.

• Regardless of the mirror type (synchronous or asynchronous), the write request is put on the mirror Write Queue for all targets that are in the Mirroring state. It is then sent to the local source volume.
  • If the type of any targets in the Mirroring state is synchronous, then the write operation is not acknowledged as complete to the process that issued the write until the source disk write completes and notification from all Synchronous mirror targets are received.
  • If the type of all targets in the Mirroring state is asynchronous, then the write operation is acknowledged as complete to the process that issued the write when the source disk write completes.
  • Should an error occur during network transmission or while the target system executes its write, the write process on the target is terminated and the state of the mirror is changed to Paused. The source volume completes the write regardless of the target write status.