DAB supports the caching of encrypted files in order to optimize processing of this class of file. However, only read caching of encrypted files is supported, no write caching. Without caching, the access times when processing encrypted files are - because of the use of encryption methods - higher than when processing unencrypted files. When caching is used, DAB can further optimize the processing of encrypted files as folllows:
Reduction of the mean I/O access time for encrypted files by dispensing with encryption operations in the event of cache hits:
The I/O times can be optimized through caching.
No encryption operations need be performed for data transfers, which can be executed as cache hits. Consequently caching can also result in a considerable reduction of the I/O access times when processing encrypted files.
Encryption operations which noticeably extend the I/O path. If the accesses to an encrypted file demonstrate a good temporal locality, a large proportion of the data accesses can be performed without encryption operations.
Reduction of the mean I/O access time for encrypted files by bundling several encryption operations:
- When data is read from disk into the cache or when the cache is saved, encryption operations must always be performed. Frequent referencing of the same data in the cache rarely occurs.
- Consequently dispensing with encryption operations by means of cache hits brings little overall benefit in terms of I/O access times to encrypted files with mainly spatial locality.
- Separate execution of the encryption operations is made more efficient by bundling the encryption of multiple disk areas in one encryption operation
- The bundling of encryption operations goes hand in hand with the creation of long I/O chains, as is possible for caching with good spatial locality
- This more efficient bundling of data encryption means that caching with DAB nevertheless reduces the mean I/O time.
The same interfaces and functions are available to users for the read caching of encrypted files as is the case for unencrypted files.