Patent ID: 8341364

Claim:
An apparatus for maintaining asynchronous mirroring, the apparatus comprising: a detection module detecting insufficient storage space to store a snapshot of a logical volume in at least one of a primary storage system and a secondary storage system, wherein the primary storage system comprises the logical volume and a mirror module incrementally mirrors a write from a host to the logical volume at the secondary storage system using an asynchronous mode; and the mirror module mirroring the write to the logical volume at the secondary storage system using a backup synchronous mode in response to detecting the insufficient storage space, wherein under the backup synchronous mode the primary storage system acknowledges the write to the host in response to receiving the write from the host, mirrors the write to the secondary storage system in response to receiving the write from the host, and the secondary storage system acknowledges the mirrored write to the primary storage system in response to receiving the mirrored write.