[Bug 1601997] Re: Ubuntu 16.10+ installer uses ext4 feature 'metadata_csum' which is incompatible with older (LTS) e2fsprogs

[Simon Iremonger]

Initial comments from the email:-

a)  There is some confusion over "metadata_csum" with/without "64bit". -- Those who have 'reverted' are usually reverting BOTH flags [as I've done some places], not just metadata_csum.
My understanding is 64bit is of no benefit except support >16TB fs and to strengthen metadata_csum's [if used, which help notice dodgy disks in theory.].

b)  The business of including e2fsprogs-1.44.0 in 18.04 at tytso's
request [NON-default extra feature support may benefit Samba users etc.
later] is not addressed.

c)  Its' worth pointing-out explicitly e2fsprogs only enabled
64bit,metadata_csum 'by default' for 'everybody' within last few weeks,
Debian change was as-you-rightly-quote.

d)  Considering the above, also think outside the ubuntu-box!  What do
canonical's customers/partners expect compatibility-wise with other non-
ubuntu systems, virtualizers/ISCSI-hosts/etc (e2fsprogs 1.42 still very
common!), let alone "backports to ubuntu LTS versions" only?.

e)  My understanding from TJ in IRC is he's started doing some tests on
some datacentre cases, there are particular issues with things like
ISCSI hosts, the host system needs to fsck guest-FS and break
otherwise!.  HOPEFULLY this will appear soon and can be added to the
mail-discussion.

I can try to join email/post directly to mail if appropriate/helpful.

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https://bugs.launchpad.net/bugs/1601997

Title:
  Ubuntu 16.10+ installer uses ext4 feature 'metadata_csum' which is
  incompatible with older (LTS) e2fsprogs

Status in e2fsprogs package in Ubuntu:
  Triaged

Bug description:
  Ubuntu 16.10 installer sets metadata_csum option on ext4 partition
  which is incompatible with other LTS Ubuntu versions (12.04 LTS, 14.04
  LTS, 16.04 LTS).

  Steps to reproduce:
  1. Download Ubuntu 16.10 installation media.
  2. Install Ubuntu.
  3. Try to do fsck -fy /dev/sdX1 from other supported Ubuntu distro.

  Expected results:
  User can check and fix errors on ext4 filesystem, created on Ubuntu 16.10.

  Actual results:
  User can not check and fix errors on ext4 filesystem because of lack of 'metadata_csum' option in previous LTS Ubuntu versions.
  The only one working solution was to scan from 16.10 live install media.

  Note:
  it is known, that Dan Watkins disabled metadata_csum when creating ext4 filesystems ( see http://bazaar.launchpad.net/~daniel-thewatkins/maas-images/fix-yakkety-builds/revision/305 ). It is good solution.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.10
  Package: e2fsprogs 1.43.1-1
  ProcVersionSignature: Ubuntu 4.4.0-30.49-generic 4.4.13
  Uname: Linux 4.4.0-30-generic i686
  ApportVersion: 2.20.2-0ubuntu1
  Architecture: i386
  CurrentDesktop: Unity
  Date: Mon Jul 11 23:42:49 2016
  SourcePackage: e2fsprogs
  UpgradeStatus: No upgrade log present (probably fresh install)

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