|
|
|
|
|
|
|
Figure 9.34
A cluster of independent disks. |
|
|
|
|
|
|
|
|
9.5.5 Clusters of Independent Disks |
|
|
|
|
|
|
|
|
In this configuration (Figure 9.34), we read complete files from disk to buffer, then (without overlap) transfer them from buffer to processor. (Disk read rate = buffer (B) to processor (P) transfer rate = 2.6 ms per 4-KB block.)e.g., if file A consists of blocks A1,A2,An, then all blocks are assigned to a single drive and access to A would be: |
|
|
|
|
|
|
|
|
Suppose we have the preceding workload, f [244], where 70% of the accesses are to files of one block and the remaining files are uniformly distributed from 2 to 16 blocks. Now the expected file length E(f) is: |
|
|
|
|
|
|
|
|
where Max is the maximum number of blocks in f and f(k) is the probability that there will be exactly k blocks in f. |
|
|
|
|
|
|
|
|
If the interarrival time for requests was 40 ms and requests were uniformly |
|
|
|
|
|
