Methods and structure for improved storage system performance with write-back caching for disk drives

In a storage system having a storage controller coupled to a plurality of disk drives wherein the storage controller has a cache memory and wherein each disk drive of the plurality of disk drives has a local cache memory, a method operable in the storage controller comprising:

• receiving a write request having associated write data from an attached host device;
• in response to receiving the write request, performing the steps of;
• allocating one or more empty blocks of memory in the cache memory to store the write data;
• storing the write data in the allocated blocks and;
• marking each of the allocated blocks as a dirty block;
• determining, subsequent to receipt of the write request, that one or more dirty blocks should be flushed from the cache memory to one or more disk drives of the plurality of disk drives;
• in response to the determination to flush the one or more dirty blocks, performing the steps of:
• transferring the one or more dirty blocks to the one or more disk drives using a write-back mode of operation with the local cache memory of each of the one or more disk drives;
• and
• marking each of the transferred dirty blocks as a written block;
• determining, subsequent to the determination to flush the dirty blocks, that the written blocks should be flushed from the local cache memory of the one or more disk drives;
• in response to the determination to flush the written blocks, performing the step of:
• forcing the flushing of local cache memory of each of the one or more disk drives;
• determining subsequent to the forcing of flushing whether the flushing has succeeded or failed;
• in response to the determination that the flushing succeeded, performing the step of:
• marking each of the flushed written blocks as a clean block;
• and
• in response to the determination that the flushing failed, performing the step of:
• marking each of the flushed written blocks as a dirty block.

A method of managing cache blocks in the cache memory of a storage controller, the method comprising:

• initializing all cache blocks in an EMPTY state;
• allocating a cache block in the EMPTY state in response to receipt of a write request from an attached host;
• copying write data associated with the write request into the allocated cache block;
• transitioning the cache block to a DIRTY state in response to the steps of allocating and copying;
• sending the data in the cache block to a disk drive having a local cache memory operating in a write-back cache management mode;
• transitioning the cache block to a WRITTEN state in response to the step of sending;
• detecting successful synchronization of the content of the local cache memory of the disk drive to persistently store the cache block;
• and
• transitioning the cache block to a CLEAN state in response to the step of detecting successful synchronization.