Re: [RFC 0/13] extents and 48bit ext3

[Jeff Garzik <jeff@garzik.org>]

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