Disclosed is a 2-level cache system for a Redundant Array of Independent
Disks (RAID) device used as part of a Storage Area Network (SAN) system.
The RAID controller of the RAID device contains a level 1 cache contained
in the RAID controller RAM, and a level 2 cache is created in a
Log-structured File System (LFS) portion of a local hard disk drive of
the RAID device. The 2-level cache system provides increased data
integrity and reliability, as well as less fragmentation of the data
frame, for communications with remote storage devices in a SAN system.
The increased performance is due to data caching being done at the RAM
and disk level instead of data being sent directly to the transmit
buffer. The 2-level cache system delays data transmissions until there is
system idle time, thus, providing efficient bandwidth utilization of SAN
communications, as well as improved resource allocation at the RAID
controller level. The 2-level cache system can avoid transmissions across
the SAN communication link, thus, freeing RAID controller resources for
other purposes when the data frames do not need to be transmitted. The
level 2 cache on the log-structured file system disk records a timestamp
of each entry in the level 2 cache, making data recovery after a system
malfunction faster and easier.