CA 714 CA - Homework #2
Homework 2 is due Wednesday, 2/20/02.
This homework covers chapter 7.
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The example on page 744 assumed the RPM, seek time, MTTF, bandwidth, and
cost per GB was similar for the large disk drive and the small disk drive.
Go to a web site and find the best cost-performance 3.5 inch drive and
the best cost-performance 2.5 inch dirve. Assume in a single enclosure
you can pack 8 3.5 inch "half height" dirves (1.7 inches high), 12 3.5
inch "low profile" (1.0 inches high), or 36 2.5 inch dirves. Assume
that all have a SCSI interface so that you can connect up to 15 drives
on a string. Design the RAID organization and calculate the cost-performance
and reliability as in the example on page 752. Use parameters from
that example if you cannot find more recent information from web sites.
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Assume that we have the following two magnetic-disk configurations: a single
disk and an array of four disks. Each disk has 20 surfaces, 6526
tracks per surface and 171 sectors/track. Each sector holds 512 bytes,
and it revolves at 10,033 RPM. Use the seek time formula in the fallcy
starting on page 768, including the equations in Figure 7.51 (page 768).
The time to switch between surfaces is the same as to move the arm one
track. In the disk array all the spindles are synchronized - sector
0 in every disk rotates under the head at the exact same time - and the
arms on all four disks are always over the same track. The data is
"striped" across all four disks, so four consecutive sectors on a single-disk
system will be spread one sector per disk in the array. The delay
of the disk controller is 1ms per transaction, either for a single disk
or for the array. Assume the performance of the I/O system is limited
only by the disks and that there is a path to each disk in the array.
Calculate the performance in both I/Os per second and megabytes per second
of these two disk organizations, assuming the request pattern is random
reads of 4 KB of sequential sectors. Assme the 4 KB are aligned under
the same arm on each disk in the array.
The
disks:
-are advertised with Time_min of 0.98 ms
-are advertised with Time_avg of 7.71 ms
-are advertised with Time_max of 18.2 ms
You should
use the equations given in figure 7.51 and at the middle of page 768.
Use the advertised Time_min, Time_avg, and
Time_max to calculate a, b, and c in the equation from figure 7.51, but
use 1500 cylinders as the distance in the equation at the
middle of page 768.