btrfs requirements for Quantal

Dump of notes from UDS-Q Etherpad.

* loads of btrfs benchmarks done
 * tends to fragment write heavy loads
 * snapshots are good for the upgrade testing ^W^W^W everything
   - we have the apt-brtfs-snapshot package that we would like to use
   - and nexentra did something similar with zfs
 * a lot of space is 'reserved' for COW behaviours, knowing how much space is available is hard
 * we are doing an fsck on every boot, and it is not doing a good job either
  - fsck should not be installed as it will be used automatically if it is not going to do a good job
 * are the server still wanting this for CEPHs?
 * grub2 has btrfs support, we can boot.
  - but it is missing write support for things like 'last boot failed' -- work is designed for this
          ^ hence the " There's still that stupid message on boot "Sparse file not allowed" "
* ureadahead with btrfs?
* fedora might get it as default (wait and see)
* good for fast installation
   - move filesystem across & resize = full install in minutes
   - needs info & link to why this is the case
* hard-link limit is small for use-cases like bacula, mutt (256 in one dir? http://john.freml.in/btrfs-hard-links-limit wikipedia reports more; no reported limit for all links to one file that I have found)
* no fully implemented quota support (needs checking)

= links =
* Fsck implementation of btrfs ( "dangerdonteveruse" )
http://www.phoronix.com/scan.php?page=news_item&px=MTA2MDI
* Anyone has the link to the recent btrfs benchmarks?
btrfs on 12.04 - http://www.phoronix.com/vr.php?view=17164
various mount options - http://www.phoronix.com/vr.php?view=17187
xfs linux conf.au presentation that has some comparisions with btrfs
- paper http://xfs.org/index.php/Image:Xfs-scalability-lca2012.pdf
- video http://www.youtube.com/watch?v=FegjLbCnoBw

benchmarks: http://zinc.canonical.com/~cking/fs-test
http://btrfs.boxacle.net/

video: http://vimeo.com/15325851

https://help.ubuntu.com/community/btrfs
https://wiki.ubuntu.com/FoundationsTeam/BtrfsSupport

XFS filesystem of the future (?!) https://lwn.net/Articles/476263/

Quickly browsing cephs mailing list on gmane reveals:
* there are btrfs devs and emails cross posted to btrfs mailing list (healthy relationship)
* there are ongoing tests of using btrfs
* latest thread about ceph on top of btrfs from 3.4rc reveals btrfs bugs/warnings: http://news.gmane.org/find-root.php?group=gmane.comp.file-systems.ceph.devel&article=6082
* this means that probably btrfs is not good/recommended option for running ceph in production
* further pings needed

Work items:
engage kernel/qa/iso testing on btrfs ongoing testing: TODO
setup a precise->quantal btrfs based upgrade test in the QA lab (blocked on UTAH development): BLOCKED
document caveats, benchmarks, missing features, errors (nothing obvious is missing from https://help.ubuntu.com/community/btrfs): DONE
publicize btrfs usage to powerusers (jorge did a block post during quantal?! cycle): DONE
look at grub2 write to boot area linked as a bug report instead bug #736743: POSTPONED
investigate if btrfs is recommended for CEPH (probably not): DONE