CSE 221: Homework 3

Fall 2009

Due: Tuesday, December 1, 2009 at 3:30pm in class

1. [Snoeren] A reliability-induced synchronous write is a synchronous write that is issued by the file system to ensure that the file system's state (as represented by the system's metadata) is not left inconsistent if the system crashes at an embarrassing time.
   1. Let f be a new file created in a directory d. The file system will issue at least three disk operations to complete this operation. Ignoring any data blocks allocated for the directory or new file, what are these three disk operations for?
   2. In Unix FFS, at least two of these writes will be issued synchronously. Which are they, and what order should they be performed in? Briefly explain why.
   3. Consider the Soft Updates solution to this problem. Does it do any reliability-induced synchronous writes? If so, how does it differ from FFS? If not, why can it avoid doing so? Explain.
   4. Consider the same operation in LFS. Does LFS generate any reliability-induced synchronous writes? Explain.
   5. Consider the same operation with the Rio file cache. Does Rio generate any reliability-induced synchronous writes? Explain.

2. In 1999, Wang et al. proposed a disk drive architecture supporting a service called "eager write". Rather than update a block in place, as with normal disks, an eager writing disk simply writes to the next free block near the disk head (the disk internally keeps track of this mapping by maintaining a table mapping "logical" disk blocks to physical disk blocks). Argue whether using such a disk would improve the performance of a Log-Structured File System, hurt its performance, or make little difference.