Exam 4- 2013

When data is changed its not overwritten the new

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Unformatted text preview: , goes in the next spot in this log. When data is changed, it’s not overwritten – the new version of the data is just written to the log and the old version is left in place. To read a file, in theory, you would have to read through the entire storage device in sequence to find the most recent copy of each chunk of data. In practice, the locations of each file’s data will be stored in a fast cache on the device, so you can go straight to the data itself. Would a log-structured filesystem be a good fit or a bad fit for a flash (SSD) device? Explain. Part B: Access types (5 points) Which of the following access types is fastest on flash, and which is slowest? • Random (small) reads • Random (small) writes • Large sequential reads • Large sequential writes 4 Problem 4: RAID (20 points) You have 7 TB of unique, non-redundant data. You are planning to store it on an array of disks that are 1 TB each. Your workload has a mix of small requests, which take 12 ms on this disk, and large requests, which take 40 ms on this disk (12 ms of latency and 28 ms of transfer time). Part A: RAID 1 (10 points) Answer the following questions about constructing a RAID 1 array for your data from these disks: • How many total disks will you need? • If small accesses are evenly distributed across your disks, how many small reads can you complete per second on this array? • If small accesses are evenly distributed across your disks, how many small writes can you complete per second on this array? • How long will it take to do a single large read on this array? • How long will it take to do a single large write on this array? 5 Part B: RAID 5 (10 points) Answer the following questions about constructing a RAID 5 array for your data from these same disks: • How many total disks will you need? • If small accesses are evenly distributed across your disks, how many small reads can you complete per second on this array? • If small accesses are evenly distributed across your disks, how many small writes can you compl...
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This note was uploaded on 02/08/2014 for the course CS 351 taught by Professor Dr.suzannerivoire during the Fall '13 term at Sonoma.

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