First Pop Quiz Answers COSC 6360 Fall 2017

First question What is the main motivation for log-structured file systems? (20 points)

First question What is the main motivation for log-structured file systems? (20 points) The authors of the paper wanted to replace the numerous scattered small writes common in scientific and office workloads by fewer larger contiguous writes.

Second question Where are the imap updates written on disk? (20 points)

Second question Where are the imap updates written on disk? (20 points) On the log

Third question Assume that we recover from a disk crash by reverting the state of the file system to the state it was when the last checkpoint was created. Would this affect: The durability of updates? (20 points) YES ___ NO ___ The consistency of the file system (20 points)

Third question Assume that we recover from a disk crash by reverting the state of the file system to the state it was when the last checkpoint was created. Would this affect: The durability of updates? (20 points) YES X NO ___ The consistency of the file system (20 points) YES ___ NO X (Some updates would be lost as the file system would return to a previous consistent state.)

Fourth question Why is the write cost of LFS very sensitive to disk utilization? (20 points)

Fourth question Why is the write cost of LFS very sensitive to disk utilization? (20 points) Because the write cost of LFS is inversely proportional to the percentage of disk space that can be freed—1 – u—during the segment cleaning process

Fifth question Would you recommend using LFS for a video server with a average file size of a few hundred megabytes? (20 points) YES ___ NO ___

Fifth question Would you recommend using LFS for a video server with a average file size of a few hundred megabytes? (20 points) YES ___ NO X (Most disk writes are likely to be both very large and very sequential.)