[Bug 1601997] Re: Ubuntu 16.10 installer sets metadata_csum option on ext4 partition which is incompatible with other LTS Ubuntu versions

[Simon Iremonger]

Canonical please read Theodore Tso's Comment #4 above, and consider for
Ubuntu 18.04 LTS!

This "64bit,metadata_csum" creates compatibility-issues even with 16.04
LTS, and does not seem to provide a huge benefit [>16TB fs support,
slightly stronger metadata checksumming].

This creates all sorts of problems for compatibility/portability of filesystems, e.g.:-
* dual-booting 18.04, even previous LTS version cannot fsck the filesystem.
* "ext4 portable disks" created by 18.04 similarly same problem.
* Also consider how wide is the 64bit,metadata_csum support anyway, users may want disks to work with many distros/drivers?  Canonical's commercial-supporters may have views herein?.  -- the linked bugreport also mentions another issue with hwe-edge and LVM.

Also note, turning off the 64bit,metadata_csum when required is a total
PAIN, needing filesystem offline, fsck and tune2fs in careful
concert.....

In my view, the 16.04 LTS mke2fs.conf [ ext4{} stanza with
"auto_64-bit_support = 1" and NO "64bit,metadata_csum" in "features" ]
should be seriously-considered for 18.04 "LTS" (even if 18.10 onwards follow Debian).

As tytso says, this 'change' has been "Decision-by-Default" due to
importing a Debian upstream package, I would like Canonical to make an
'informed and considered decision' about this please!.

Hope that helps!

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

Title:
  Ubuntu 16.10 installer sets metadata_csum option on ext4 partition
  which is incompatible with other LTS Ubuntu versions

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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