LiveCDUnionFS

Revision 6 as of 2005-11-03 16:24:13

Clear message

Summary

We want to be able to optionally use UnionFS on the LiveCD (instead of devmapper with Copy-On-Write snapshots) as it's more flexible and faster. As it works on the file system level, removing files added to the writable part of the file system will reduce the size, not add further to it (as it will with devmapper-based copy-on-write snapshots). Also, unionfs allows us to stack more file systems on top of each other, which could be useful from the user's point of view.

Rationale

  • Pros:
    • Faster than devmapper with copy-on-write
    • More flexible since it allows multiple levels of mounts
    • Works on the file system level which means removing files from the snapshot reduces memory usage.
  • Cons:
    • Requires patching a new FS into our kernel.
    • Has a bad history stability wise.

Due to the history of instability and the fact that instability in UnionFS will take down the box, we want to make the LiveCD's use of UnionFS optional, and leave the current devmapper + COW solution available as a fall back option.

Implementation

  • The unionfs driver needs to be added back to the kernel for Dapper: http://bugzilla.ubuntu.com/show_bug.cgi?id=9757

    • XXX: JamesTroup: maybe mention that this is due for upload soon, to save people following the link + reading the history?

  • Merge tollef.fog.heen@canonical.com/casper--unionfs--0 with the current casper.

    • XXX: JamesTroup: what does this code do?  Is it complete?  Does it make UnionFS optional?  Has it been tested, etc.?

  • Test according to FormalTestPlans

  • While bugs are still present: fix bugs and retest
  • Release
  • Profit