Write cache recovery after loss of power
View Patent ↗A method for recovering dirty write cache data after controller power loss or failure from one of two independently battery backed up and mirrored write caches. Two independent controllers jointly operate with a permanent data storage system. Each controller has a write cache that is a mirror of the write cache in the other controller. The primary controller resets a power down flag stored each write cache upon proper shutdown. The primary controller further increments and stores a configuration sequence number into each write cache upon proper shutdown. If a primary controller powers up and identifies that the write cache was not properly shutdown due to the state of the power down flag, it flushes the dirty data in the write cache only if the configuration sequence number contained in the write cache is the same as the configuration sequence number contained in the primary controller. If the configuration sequence number in the primary controller is higher than the configuration sequence number in the write cache, the dirty data was previously flushed to permanent data storage with the other write cache.
1. A method of recovering dirty write cache data after loss of power to a primary controller associated with a write cache, comprising:
providing means for retaining information in the write cache in absence of controller power;
verifying whether a power down flag stored in the write cache indicates that the write cache was not properly shutdown;
verifying whether a configuration ID stored in the write cache matches a configuration ID stored in the controller;
verifying whether a configuration sequence number stored in the write cache corresponds to a configuration sequence number stored in the controller; and
flushing dirty data present in the write cache to a permanent data storage system when the power down flag indicates that the write cache was not properly shutdown, the configuration ID matches that stored in the primary controller and the configuration sequence number matches the configuration sequence number stored in the primary controller.
2. The method of claim 1 further including incrementing the configuration sequence number stored in the primary controller upon a proper shutdown and storing the configuration sequence number in the write cache if the write cache's configuration ID matches the configuration ID stored in the primary controller.
3. The method of claim 2 further including storing the configuration sequence number in the write cache of a backup controller if the write cache's configuration ID matches the configuration ID stored in the backup controller.
4. The method of claim 2 further including incrementing the configuration sequence number stored in the primary controller upon power up and storing the configuration sequence number in the write cache if the write cache configuration ID matches the configuration ID stored in the primary controller.