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Migrating to ext4

To celebrate the stabilization and release of Ubuntu 9.04, I’ve destabilized my primary (work and personal) laptop a bit by migrating from ext3 to ext4, following (more or less) the procedure I found on the ext4 wiki.  I created a fresh 9.04 USB stick with usb-creator, booted it, ran the procedure, mounted the filesystem, updated /etc/fstab, and rebooted from the internal disk.

In order to try out the delayed allocation feature, I re-allocated (via cp/mv) some parts of my disk which I thought might benefit from being less fragmented, such as:

  • *.sqlite in my Firefox profile directory (urlclassifier3.sqlite went from hundreds down to 3 extents)
  • the .iso files I use for testing Ubuntu in KVM (ubuntu-9.04-desktop-i386.iso went from 2391 down to 71)
  • my mutt cache (discovering in the process that it now uses a different format, so I couldn’t compare)

(note: filefrag(8) will tell you how fragmented a file is)

I expect that defragmenting my system libraries and other startup data would get my system booting a bit faster, but I think I’ll just let that happen naturally when I upgrade to Karmic.

I did some stress testing by running a large offlineimap update while starting up Firefox and deleting some large files, and was rewarded with a solidly frozen system (no network response, no caps lock, no response to SysRq).  I could not get any information about the cause of the crash, though the proximity to the ext4 switch is certainly suspicious…

Onward to Karmic!


Written by Matt Zimmerman

April 26, 2009 at 20:56

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14 Responses

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  1. You may be look at bug 330824 .


    April 26, 2009 at 22:23

    • Quite possibly, thanks for the reference.


      April 26, 2009 at 22:42

  2. Phil

    April 26, 2009 at 22:26

  3. Leon Nardella

    April 26, 2009 at 23:44

    • I was aware of that one, and understand that it has been addressed by patches the kernel team pulled into the 9.04 kernel. There may of course be other data corruption bugs.


      April 27, 2009 at 09:08

  4. I hope you’re being super good at backing up your data. I tried running / as ext4 in the jaunty alpha stage but it was trashed by some or other bug – I didn’t have the skill to diagnose what happened, and no one was on IRC at the time who could help. I’m very glad I didn’t convert /home. I’m back to ext3 for now.

    Damon Lynch

    April 27, 2009 at 03:57

    • My irreplaceable data lives on servers which get backed up. Although this is the machine I usually type on when I’m working, it doesn’t contain anything essential. After all, it’s a laptop, and I take it with me while traveling, so it could get lost.


      April 27, 2009 at 09:10

  5. As long as the ext4 developers fail to understand that people are going to run KDE and GNOME, however badly-written, on top of their wonderful file system, I fear I’ll be sticking with ext3.

    David Gerard

    April 27, 2009 at 20:12

    • We’re actually very pleased with how well they are working with us. While we are discovering problems (which is to be expected), they’ve responded quickly and helped to diagnose them. Ted Ts’o in particular has been very involved and helpful as we’ve made ext4 available in Ubuntu.

      Maybe we’ll need to fix some programs, and maybe we won’t, but I’m confident we’ll converge on a solution which works for everyone.


      April 28, 2009 at 09:35

  6. […] Matt Zimmerman talks about his experience migrating to ext4 […]

  7. After upgrading my kernel to the latest one in -proposed, I discovered a missing step: grub-install (hd0)

    The version of grub installed in my MBR did not know how to read ext4 extent maps, but the version in the 9.04 grub package does. The above command installs the new version.


    April 30, 2009 at 08:14

  8. Two months in, I’m very satisfied with ext4. The bug I experienced is fixed in Karmic, and I haven’t had any other problems.


    June 21, 2009 at 11:34

    • Yeah, but still open in Jaunty. :(
      /me using a kernel from the mainline builds ppa


      June 21, 2009 at 16:34

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