Abstract: A storage-controller-managed outboard incremental backup/restore of data. An indicator is assigned to an associated portion of data stored in a data storage device, wherein the indicator resides in a memory of a storage controller coupled to the data storage device. A value of the indicator residing within the memory of the storage controller is set when the associated portion of the data has changed. The associated portion of the data stored in the data storage device is backed using the storage controller when the value of the indicator residing within the memory of the storage controller is set. The value of the indicator residing within the memory of the storage controller is cleared when the associated portion of the data has been backed up.

Abstract: A system manages data transfer between a computer, a data storage disk, and a data buffer which is associated with the disk. Upon receipt of a write request during data read-ahead from the disk to the buffer, the system preempts the read-ahead to write the data to the disk only when the target write track on the disk is different from the track being read ahead into the buffer. Otherwise, the system permits read-ahead to continue until the target write sector is positioned beneath the disk drive head. Also, upon receipt of a read request during cache writing from the buffer to the disk, the system immediately satisfies the read request prior to completing the cache writing when the requested read data is contained in the buffer. Moreover, the system provides for dynamic switching between a data read-ahead preempt policy and a data read-ahead no-preempt policy based upon parallel monitoring and comparison of data request service times under both policies.

Abstract: A disaster recovery system providing asynchronous remote data shadowing between a primary and a secondary site uses a pair of track arrays for each primary data storage device of a remote copy pair to monitor which record updates are in transit between the primary site and the secondary site. A host processor at the primary site of the disaster recovery system transfers a sequentially consistent order of copies of record updates to the secondary site for back-up purposes. The copied record updates are stored on the secondary data storage devices which form remote copy pairs with the primary data storage devices at the primary site. One track array, the active track array, is used to set elements according to which tracks on the primary data storage device receive record updates from the host processor at the primary site.