With a non-rotor guarantee, the eight drives would be given an optimal I/O size of 512 KB. Each drive can support seven such operations each second. The higher rate (7 x 512 KB versus 23 x 64 KB) is achievable because the larger transfer size does less seeking. Again the drives would be arranged in an eight-way stripe but with a stripe unit of 512 KB. Each drive can support seven 512K streams per second for a total of 8 * 7 = 56 streams. Each of the 56 streams is given a time period (also known as a time "bucket"). There are eight different time periods with seven different processes in each period. Therefore, 8 * 7 = 56 processes are accessing data in a given time unit. At any given second, the processes in a single time period are allowed to access only a single disk.
Using a rotor guarantee more than doubles the number of streams that can be supported with the same number of disks. The tradeoff is that the time tolerances are very stringent. Each stream is required to issue the read/write operations within one time quantum. If the process issues the call too late and real-time scheduling is used, the request blocks until the next time period for that process on the disk. In this example, this could mean a delay of up to eight seconds. In order to receive the rate guarantee, the application must access the file sequentially. The time periods move sequentially down the stripe allowing each process to access the next 512 KB of the file.