Distributed safe data commit in a data storage system

A storage controller for use with a plurality of units of storage in which each unit of storage has a plurality of subunits of storage, comprising:

• a cache;
• and
• distributed safe data commit logic having at least one of software, firmware and hardware wherein said at least one of said distributed safe data commit logic is configured to destage data stored in the cache which has not yet been destaged for storage to an associated subunit of storage of a unit of storage to ensure destaging to storage of data written to the cache prior to a safe data commit scan start time, the distributed safe data commit logic including:
• scan logic configured to identify a subunit of storage for which there is data stored in cache which has not yet been destaged for storage to the associated subunit of storage of a unit of storage;
• and
• allocation logic having at least one of software, firmware and hardware wherein said at least one of said allocation logic is configured to identify the unit of storage of the identified subunit of storage and to allocate a task control data structure of a first type to destage the data of the identified subunit of storage to the unit of storage in a destage operation unassociated with host input/output operations, in response to a total of the task control data structures of the first type allocated to the identified unit of storage of the identified subunit of storage remaining within a first task control block (TCB) type allocation limit imposed for a total of task control data structures of the first type allocated to the identified unit of storage wherein the task control data structure of the first type is a background task control block (TCB) unassociated with host input/output operations and excludes a foreground task control block (TCB) otherwise associated with host input/output operations so that allocation of background TCBs is prioritized over allocation of foreground TCBs for destage operations for the identified unit of storage, and to allocate a task control data structure of a second type to destage the data of the identified subunit of storage to the unit of storage in a destage operation unassociated with host input/output operations, in response to a total of the task control data structures of the first type allocated to the identified unit of storage of the identified subunit of storage reaching the first TCB type allocation limit imposed for a total of task control data structures of the first type allocated to the identified unit of storage wherein the task control data structure of the second type is a foreground task control block (TCB) associated with host input/output operations unless the identified subunit of storage has reached the first TCB type allocation limit imposed for the total of task control data structures of the first type allocated to the identified unit of storage so that a foreground task control block (TCB) is allocated to destage the data of the identified subunit of storage to the unit of storage in a destage operation unassociated with host input/output operations, instead of being allocated for an operation associated with an input/output operation from a host.

A method for use with a plurality of units of storage in which each unit of storage has a plurality of subunits of storage, comprising:

• safe data commit processing a cache to ensure destaging to storage of data written to the cache prior to a safe data commit scan start time, the safe data commit processing including:
• identifying a subunit of storage for which there is data stored in cache which has not yet been destaged for storage to the subunit of storage of a unit of storage;
• identifying the unit of storage of the identified subunit of storage;
• allocating a task control data structure of a first type to destage the data of the identified subunit of storage to the unit of storage in a destage operation unassociated with host input/output operations, in response to a total of the task control data structures of the first type allocated to the identified unit of storage of the identified subunit of storage remaining within a first task control block (TCB) type allocation limit imposed for a total of task control data structures of the first type allocated to the identified unit of storage wherein the task control data structure of the first type is a background task control block (TCB) unassociated with host input/output operations and excludes a foreground task control block (TCB) otherwise associated with host input/output operations so that allocation of background TCBs is prioritized over allocation of foreground TCBs for destage operations of the safe data commit process for the identified unit of storage;
• and
• allocating a task control data structure of a second type to destage the data of the identified subunit of storage to the unit of storage in a destage operation unassociated with host input/output operations, in response to a total of the task control data structures of the first type allocated to the identified unit of storage of the identified subunit of storage reaching the first TCB type allocation limit imposed for a total of task control data structures of the first type allocated to the identified unit of storage wherein the task control data structure of the second type is a foreground task control block (TCB) associated with host input/output operations unless the identified subunit of storage has reached the first TCB type allocation limit imposed for the total of task control data structures of the first type allocated to the identified unit of storage so that a foreground task control block (TCB) is allocated to destage the data of the identified subunit of storage to the unit of storage in a destage operation unassociated with host input/output operations, instead of being allocated for an operation associated with an input/output operation from a host.