Patent ID: 7975169

Claim:
A method for preserving data in a storage subsystem having dual cache and dual nonvolatile storage (NVS) through a failover from a failed cluster to a surviving cluster, comprising: initiating a memory preserved indicator to mark tracks on a cache of the surviving cluster to be preserved, the tracks having an image in an NVS of the failed cluster; performing a destage operation to destage the marked tracks from the cache of the surviving cluster to disk, wherein: if one or more ranks associated with the marked tracks is determined to be in a good state, the marked tracks are destaged, otherwise if available space is located the marked tracks are retro-restored to the NVS of the surviving cluster, otherwise the marked tracks are pinned in the cache of the surviving cluster; and subsequent to a determination that each of the marked tracks have been destaged, disabling the memory preserved indicator to remove the mark from the tracks, wherein if the surviving cluster reboots previous to each of the marked tracks having been destaged: the cache of the surviving cluster is verified as a memory preserved cache, the marked tracks are retained for processing while all unmarked tracks are removed, and the marked tracks are processed.