Preservation of cache data following failover

A data storage subsystem configured to store data with respect to at least one host adapter, comprising:

• disk storage configured to store data;
• and
• a pair of clusters, each comprising:
• local non-volatile data storage;
• local cache data storage;
• and
• subsystem control configured to store dual mode DASD fast write data of a logical subsystem in said local non-volatile data storage and dual mode DASD fast write data of another logical subsystem in said local cache data storage;
• and, in response to a failover of one of said pair of clusters to a local cluster, to convert said local cache storage dual mode DASD fast write data to converted fast write data and to attempt to destage said converted fast write data from said local cache data storage to said disk storage, and said subsystem control is configured to, in response to failure to destage said converted fast write data to said disk storage, allocate local non-volatile storage tracks and emulate a host adapter to provide said converted fast write data of said local cache data storage to said local non-volatile storage for storage by said local non-volatile storage, reconverting said converted fast write data of said local cache data storage to local single mode DASD fast write data stored in said local non-volatile storage and stored in said local cache storage.

A cluster of a pair of clusters of a data storage subsystem, said data storage subsystem configured to store data with respect to at least one host adapter and a disk storage configured to store data;

• said cluster comprising a local cluster comprising:
• local non-volatile data storage;
• local cache data storage;
• and
• subsystem control configured to store dual mode DASD fast write data of a logical subsystem in said local non-volatile data storage and dual mode DASD fast write data of another logical subsystem in said local cache data storage;
• and, in response to a failover of one of said pair of clusters to said local cluster, to convert said local cache storage dual mode DASD fast write data to converted fast write data, and to give priority to said converted fast write data over other fast write data for destaging said data to said disk storage.

A cluster of a pair of clusters of a data storage subsystem, said data storage subsystem configured to store data with respect to at least one host adapter and a disk storage configured to store data;

• said cluster comprising a local cluster comprising:
• local non-volatile data storage;
• local cache data storage;
• and
• subsystem control configured to store DASD fast write data of a logical subsystem in said local non-volatile data storage and DASD fast write data of another logical subsystem in said local cache data storage;
• and, in response to a failover of one of said pair of clusters to said local cluster, to convert said local cache storage dual mode DASD fast write data to converted fast write data and to attempt to destage data from said local cache data storage to said disk storage, and said subsystem control is configured to, in response to failure to destage said converted fast write data to said disk storage, allocate local non-volatile storage tracks and emulate a host adapter to provide said converted fast write data to said local non-volatile storage for storage by said local non-volatile storage, reconverting said converted fast write data of said non-volatile storage to local DASD fast write data stored in said local non-volatile storage and stored in said local cache storage.

A method for operating a local cluster of a pair of clusters comprising a data storage subsystem, said data storage subsystem configured to store data with respect to at least one host adapter and comprising disk storage configured to store data;

• said cluster comprising local non-volatile data storage;
• local cache data storage;
• and subsystem control;
• said method comprising the steps of:
• storing DASD fast write data of a logical subsystem in said local non-volatile data storage and storing DASD fast write data of another logical subsystem in said local cache data storage;
• in response to a failover of one of said pair of clusters to said local cluster, converting said local cache storage DASD fast write data to converted fast write data;
• and
• in response to failure to destage said converted fast write data to said disk storage, allocating local non-volatile storage tracks and emulating a host adapter to provide said converted fast write data to said local non-volatile storage for storage by said local non-volatile storage, thereby reconverting said converted fast write data of said non-volatile storage to local DASD fast write data stored in said local non-volatile storage and stored in said local cache storage.

A computer program product comprising a computer useable medium having computer useable program code tangibly embodied therein for operating a local cluster of a pair of clusters comprising a data storage subsystem, said data storage subsystem configured to store data with respect to at least one host adapter and comprising disk storage configured to store data;

• said local cluster comprising local non-volatile data storage;
• local cache data storage;
• and subsystem control, said subsystem control storing DASD fast write data of a logical subsystem in said local non-volatile data storage and storing DASD fast write data of another logical subsystem in said local cache data storage;
• said computer useable program code configured to, when executed on said subsystem control, cause said subsystem control to:
• in response to a failover of one of said pair of clusters to said local cluster, convert said local cache storage DASD fast write data to converted fast write data;
• and
• in response to failure to destage said converted fast write data to said disk storage, allocate local non-volatile storage tracks and emulate a host adapter to provide said converted fast write data to said local non-volatile storage for storage by said local non-volatile storage, thereby reconverting said converted fast write data of said non-volatile storage to local DASD fast write data stored in said local non-volatile storage and stored in said local cache storage.