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    SubjectRe: [Ext2-devel] [RFC 0/13] extents and 48bit ext3
    Andreas Dilger wrote:
    > Except that the only way that they will get extents is if they read some
    > documentation that tells them to mount with "-o extents", which will also
    > say "this is incompatible with older kernels - only use it if you aren't
    > going to revert to older kernels". If they try to mount such a filesystem
    > it will report "trying to mount filesystem with incompatible feature",
    > and "e2fsprogs" will report "incompatible feature extents - please upgrade
    > your e2fsprogs" (for versions newer than Nov 2004).

    False. What will happen is that distros will default to extents, and
    users will continue to not read documentation, as usual.


    > It's a lot better than e.g. the latest ubuntu which (apparently,
    > I read) can't mount a kernel older than 2.6.15 because of udev (or
    > sysfs?) changes. It's better than e.g. reiserfs vs. reiser4 compatibility
    > (which doesn't exist). 2.4 kernels probably can't mount a new udev root
    > filesystem because none of the /dev files exist either. 2.4 kernels can't
    > mount a filesystem that is using device mapper ("LVM 2.0") instead of
    > "LVM 1.0". All 2.2 kernel.org kernels couldn't use any system with RAID,
    > because any distro worth its salt had upgraded the RAID code to a working
    > (incompatible) version.

    This is different.

    The proposal is to change the thing called "ext3" to suddenly require
    kernels >= 2.6.18, while still calling it "ext3."

    The above examples are actually proving my point. The above examples
    had much more clear distinctions between incompatible upgrades.


    > Nobody is forcing users to use extents. Same with large inodes in ext3,
    > which give a 7x speedup in samba4 performance - did this cause you any
    > heartburn yet? Large inodes + fast EAs are available for people who want
    > to use it for a couple of years already, will soon allow nanosecond times
    > and maybe one day in the distant future it will become the default but not
    > yet. In a few years, the support for extents in ext3 will be pervasive
    > and most people won't care if they can boot to 2.4.10 or not, and if they
    > care about this they will also know enough not to enable extents. The ext3
    > developers are a very cautious bunch, and don't force anything onto users.

    I wouldn't use the word "cautious" to describe continually adding new,
    incompatible features to the main Linux filesystem.

    You are as cautious as one can be, while adding potentially
    destabilizing features.

    Jeff


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