Cache protection through cache

A non-transitory computer readable storage medium storing computer software for providing cache coherency protection, the computer software comprising:

• executable code that receives a data write request for a data block at a first director from a host;
• executable code that, immediately in response to receiving the data write request, and independent of any subsequent read request or write request:
• stores the data block in a cache of the first director;
• transmits a copy of the data block from the first director to a second director;
• and
• stores the copy of the data block in a cache of the second director;
• executable code that maintains a directory that identifies a location of the data block;
• executable code that locally services a read request using the data block or the copy of the data block stored in the cache of one of the first director or the second director;
• and
• executable code that initiates a failure recovery process in response to failure of the first director by using the data block or the copy of the data block stored in the cache of the second director, and a third director operates as a protection partner of the second director during the failure recovery process of the first director and until the first director returns to operation and the first and second directors become protection partners;
• and
• executable code that initiates a failure recovery process in response to failure of the second director by using the data block or the copy of the data block stored in the cache of the first director, and a third director operates as a protection partner of the first director during the failure recovery process of the second director until the second director returns to operation and the first and second directors become protection partners.

A system for providing cache coherency protection, comprising:

• a first director having at least one processor and a cache;
• a second director having at least one processor and a cache, wherein, immediately in response to the first director receiving a data write request for a data block from a host, and independent of any subsequent read request or write request, the data block is stored in the cache of the first director, a copy of the data block is generated by the first director and transmitted to and stored on the cache of the second;
• a directory that identifies a location of the data block, wherein the directory is distributed among at least the first director and the second director;
• and
• a processor that performs the following:
• in response to a read request received at a respective one of the first director or the second director for the data block, locally servicing the read request using the data block or the copy of the data block stored in the cache of the respective one of the first director or the second director;
• in response to failure of the first director, a failure recovery process is initiated using the data block or the copy of the data block stored in the cache of the second director, and a third director operates as a protection partner of the second director in place of the first director during a failure recovery process until the first director returns to operation and the first and second directors become protection partners;
• and
• in response to failure of the second director, the failure recovery process is initiated using the data block or the copy of the data block stored in the cache of the first director and the third director operates as a protection partner of the first director in place of the second director during the failure recovery process until the second director returns to operation and the first and second directors become protection partners.