Two main goals of parallelism in a disk system:
1. Load balance multiple small accesses to increase throughput
2. Parallelize large accesses to reduce response time.
Improve transfer rate by striping data across multiple disks.
Bit-level striping – split the bits of each byte across multiple disks
In an array of eight disks, write bit i of each byte to disk i.
Each access can read data at eight times the rate of a single disk.
But seek/access time worse than for a single disk
Bit level striping is not used much any more
Block-level striping – with n disks, block i of a file goes to disk (i mod n) + 1
Requests for different blocks can run in parallel if the blocks reside on different disks
A request for a long sequence of blocks can utilize all disks in parallel