Paper-5: LFS

Read Chap-43 of "Operating Systems: Three Easy Pieces" by Remzi H. Arpaci-Dusseau and Andrea C. Arpaci-Dusseau. This chapter describes a log-structured file system.

The Log-Structured File System departs dramatically from the UNIX File System and proposes, instead, a file system in which all of the data is stored in an append-only log, that is, a flat file that can be modified only by having data added to the end of it. In Chapter 9, we also hear about logs, specifically how they help achieve reliability. For today's reading, the purpose of the log is to achieve good performance.

Please answer the following questions:

• Why an append-only log might lead to high performance?
• How does the log-structured file system minimize seeks and write in large batches?
• Reads are likely to cause a seek. How to ensure the performance of read?
• In the log structured file system all the changes are made by writing on to the end of the log, including changed inodes. During normal operation the inode map in memory keeps track of where the current version of an inode is located in the log. After a crash the inode map is lost. How does it get reconstructed?
• Are there certain file access patterns by applications that might make it hard for a log-structured file system to avoid seeks?

Take your time preparing for this. You are required to hand in your answers before 23:59 on 27 Dec, 2018.