Comp111: Operating Systems
Classroom Exercise 18
Fall 2017

group member 1: ____________________________ login: ______________
group member 2: ____________________________ login: ______________
group member 3: ____________________________ login: ______________
group member 4: ____________________________ login: ______________
group member 5: ____________________________ login: ______________
group member 6: ____________________________ login: ______________
group member 7: ____________________________ login: ______________
group member 8: ____________________________ login: ______________

  1. Journals preserve consistency by entering special records called "consistency watermarks" into the journal whenever the filesystem is in a consistent state. How can this be used to restore a filesystem after a crash?

  2. Suppose that I recover from a crash by reconciling a journal (to the last consistency watermark) and -- before I'm done -- the system crashes again. How does one recover from the second crash?

  3. In an EXT3 filesystem (which can be thought of as like EXT2, but with bigger inodes, addresses, and a journal), what happens to block read time when a journal is used. Does it stay the same or increase or decrease? Why?
  4. In the "pure" journalling ("transactional filesystem") approach, in which the whole disk is a journal, what happens as the disk fills up?

  5. Is a file erased when its directory entry is erased? Why or why not? What does it take to truly "erase" a file?

  6. In a raid 5 filesystem, reads become slower when a disk fails. Why?

  7. (Advanced) In a flash drive with virtualized blocks, private data cannot be erased efficiently. Why?