LiveCDUnionFS

Differences between revisions 4 and 5
⇤ ← Revision 4 as of 2005-11-02 22:35:28 →
Size: 885
Editor: 209
Comment: Ask for review again
← Revision 5 as of 2005-11-02 23:15:52 → ⇥
Size: 2546
Editor: 209
Comment: review
Deletions are marked like this. Additions are marked like this.
Line 12: Line 12:
{{{XXX: JamesTroup: full marks for brevity, less marks for usefulness. Without a rationale, this spec is very hard to decode.
                    How is it more flexible than devmapper? "appears to be faster in some cases" isn't exactly a ringing
                    endorsement. Can we really not be more conclusive than that? The structure is also sub-optimal,
                    I'd suggest something more like the below, but expanded with better info on how it's more flexible and why
                    we want it. I realise you've already done the implementation work, but this spec will be around forever
                    and should be useful in helping us remember why we switched.}}}

== SuggestedSummary ==

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.

== SuggestedRationale ==

 * Pros:

  * More flexible because it allows us to do foo.
  * More flexible because it allows us to have bar.
  * Is faster when doing baz.

 * 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.
Line 15: Line 41:
   {{{XXX: JamesTroup: maybe mention that this is due for upload soon, to save people following the link + reading the history?}}}
Line 16: Line 43:
   {{{XXX: JamesTroup: what does this code do? Is it complete? Does it make UnionFS optional? Has it been tested, etc.?}}}

Summary

UnionFS is more flexible than using devmapper with copy-on-write snapshots. Casper should support both devmapper as well as unionfs. UnionFS also appears to be faster in some cases. UnionFS used to oops a lot, so we want a fallback.

{{{XXX: JamesTroup: full marks for brevity, less marks for usefulness. Without a rationale, this spec is very hard to decode.

  • How is it more flexible than devmapper? "appears to be faster in some cases" isn't exactly a ringing endorsement. Can we really not be more conclusive than that? The structure is also sub-optimal, I'd suggest something more like the below, but expanded with better info on how it's more flexible and why we want it. I realise you've already done the implementation work, but this spec will be around forever and should be useful in helping us remember why we switched.}}}

SuggestedSummary

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.

SuggestedRationale

  • Pros:
    • More flexible because it allows us to do foo.
    • More flexible because it allows us to have bar.
    • Is faster when doing baz.
  • 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

LiveCDUnionFS (last edited 2008-08-06 16:35:07 by localhost)