Research And Design Of A RAID System With Fibre Channel Interface

DAS, SAN and NAS are three kinds of network storage architectures which are widely used at present. RAID plays an important role as nodes of the storage network, the design of which can determine the performance of the whole storage architecture.The design of RAID system is composed of the embedded hardware platform, software platform, and kernel algorithm software. The design of embedded hardware platform refers to Intel IQ31244 board, which adopts independent IOP processor, high speed bus and interfaces. On one hand, RAID system communicates with external hosts with high speed fibre channels, on the other hand, internal devices of RAID system connect with PCI-X bus for data transmission, which provides sufficient bandwidth.The embedded hardware platforms are always customized for special application, which is different from X86 that has general specification. The software platform for embedded RAID system are composed of BSP Redboot, linux kernel and root filesystem, which implements initialization for hardware platform, and provides the running environment for kernel algorithm software.As the design of kernel algorithm software, the target supports Fibre Channel transmission protocols, and provides high speed connection between RAID system and external hosts; CACHE management applys Hash Links for organization and search of data stripes, and it implements tactics of data prefetch, LRU elimination, conflication control, variable granularity of access blocks and write through or write back; compared with tranditional disk I/O schedule, the new I/O schedule adds high and low priority queues. Normal I/O commands enter high priority queue and are handled first, instead transactions of data backup and journal enter low priority queue and are handled with delay, which is beneficial to shorten the response time between RAID system and external hosts; hardware xor accelerates the speed of frequent data parity operations, speeds up the I/O command process, and reduces the calculation burden of CPU.The prototype of RAID system is implemented as the design above, and the peak data transmission speed of the prototype system is 186MB/s, which is little higher than the speed 179MB/s of the same type production NexStor 4250F. The data transmission speed is close to the 2Gb/s bandwidth of fibre host channel. The test result prove that the design and implementation of prototype of RAID system are feasible.