Research Of The Data Scheduling Strategy For Flash-Disc Hybrid Disk

The performance of the hard disk has significant impact on the whole computer system. But it has been dropped behind and turns to be the bottleneck. This is because that the real I/O speed of the hard disk is limited by the magnetic head's read/write speed. In order to solve this problem, flash and hard disk can be assembled to constitute hybrid hard disk. By caching the data in and out the disk in the flash, the hybrid hard disk will have better performance. For the data to be written into the disk, the flash will cache the data until the data size is up to a fixed value; for the frequently used data read from the disk, the flash also caches the data for the purpose of avoiding read the same data from the disk when it is used next time. Also, when there are no operations to the disk, the disk sheet can be spin down to reduce the consumption of energy.In the hybrid hard disk, the flash is the cache of the disk. Its level is between the main memory and the disk. As cache, flash is different from the traditional RAM style cache, because it won't lose the data in it when the power is suddenly down. So this point makes accelerating the computer's power on rate possible.The key problem of the hybrid hard disk is to design proper scheduling strategy and algorithm. Through analyzing all kinds of cache technology and the storage management strategy, special scheduling strategy is designed to the hybrid hard disk. The space of the flash is divided to parts -- read cache and write cache. The main work is concerned on finding the requested data block quickly, arranging the space pieces which has affect on transport speed, replacing the old data with new requested data, prefetching data fast and effectively, judging when to spin down or spin up the disk.By emulating the performance of the hybrid hard disk, hybrid hard disk makes progress in transporting rate, power consumption and reliability.