| 摘要 |
A data storage system includes a computer coupled to a non-volatile storage, such as a disk drive, through an interconnect. The computer may include a block cache for storing cached copies of data blocks, and a hash table that stores hash values corresponding to the data blocks. Prior to writing back a modified cache block to the non-volatile storage, a log recorder of the computer stores an updated hash value corresponding to the modified cache block within a write-ahead hash log, which may also be also contained in non-volatile storage. In one particular implementation, the log recorder may create a log record including an updated hash value and an address corresponding to a modified cache block. The log recorder may additionally maintain a first pointer value indicative of log records that have been stored to the write-ahead hash log, and a second pointer value indicative of the most recent log record stored in the write-ahead hash log for which a corresponding modified cache block has been stored to the non-volatile storage. These pointer values may be stored in the write ahead hash log with the log records. Log records may be grouped into log blocks which are eventually written to the non-volatile storage as a group. After the log record containing the updated hash value has been successfully written to write-ahead hash log, a cache manager may initiate the write-back of the dirty data block to the non-volatile storage. Until a verification has been made to ensure the corresponding dirty data block has been successfully written back to non-voliatile storage, the old hash value for the data block may also be retained in the write-ahead hash log. If a system, network or disk failure occurs between the writing of the log record containing the updated hash value to the write-ahead hash log and the writing of the corresponding dirty data block to the non-volatile storage, the hash table may be rebuilt according to the records in the write-ahead hash log. |
