## Quiz 37

Three questions, submit as "quiz37".  Due 2:45pm before lecture 11/30/2007.

If you are confused as to the difference between 1MB (1,000,000B) and 1MiB (1,048,575B) you may wish to read this: Wikipedia: Binary Prefix. We will be lenient on the different when grading this quiz.

### 1.

Suppose we want to send some files from one laptop to another over a wireless network.
• We have 100 files of 40MiB each.  (1MiB = 1,048,576B)
• The wireless network has a bandwidth of 5Mbit/s.  (1Mb = 1,000,000b)
• The laptop battery holds 100kJ (100,000 joules) of energy.
• The wireless network card consumes 5W (5 watts) while transmitting, and the remained laptop consumes 35W no matter what.
• Before each file transfer, we need 10s to decide which file to send.
How many files will we get to finish sending before the battery is completely empty? Show at least some of your work.

Consider two RAID disk systems that are meant to store 10 tebibytes (1TiB = 1024GiB = 10244B) of data.
1. System A uses RAID 1.
2. System B uses RAID 5 with 4 disks in the protection group.

### 2.

If reading or writing any one block of a disk takes 30ms, how long will it take to write a single block to System B in the worst case? Answer in ms. You may assume that accesses to two different disks may be done in parallel.

### 3.

Which system is more reliable? Please explain very briefly.