Consider a disk array with 12 identical disks. Each of the disks in the array ha

Question

Consider a disk array with 12 identical disks. Each of the disks in the array has 10 double-sided platters with 512 bytes sectors, a block size of 1KB, 14850 tracks per surface, 500 sectors per track, average seek time of 12msec, 7200 rpm(revolutions per minute), and transfer rate of 36 MB/sec. With this information, answer the following four questions:

1. What is the capacity of one disk of the array?

2. What is the capacity of a cylinder?

3. How long it takes to read 36 MB of data from disk number 5 if the I/O occurs using a sequential access pattern? Hint: Interpret rotational delay as worst case scenario.

4. What is the max time it will take to read 39 blocks of data from disk number 1 if the I/O occurs using a random access pattern? Hint: Interpret rotational delay as worst case scenario.

Explanation / Answer

The set of all the tracks in the same relative position on the platter is referred to as a cylinder.

capacity of the cylinder is = byte/sector*avg.sector/track/surface*surface/platter*platter/disk

512 bytes sectors, a block size of 1KB, 14850 tracks per surface, 500 sectors per track, average seek time of 12msec, 7200 rpm so capacity is 512*500*14850*10= 38.1 gb

capacity of 1 disk is 500/512= .976 bytes

time required to read 36 mb is 60/rpm i.e 60/7200*1/500=0.01ms

max time to read 39 block of data is 0.01*39=0.39ms

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