-o extents (ext4 capabilities for newly-created files)

[Theodore Tso]

On Sun, May 31, 2009 at 09:07:05PM +0300, David Baron wrote:
> Is it desirable to use this to make current ext3 filesystems hybrid ext4 
> systems?

You will get some of the benefits of ext4, without having to do a
dump/restore.

> Is there any advantage to extents for numerous, non-huge, more normal-sized 
> files.

Define "non-huge".  If the file is less than 48k on a 4k block
filesystem, it doesn't make difference.  For files larger than 48k, it
is likely, if the filesystem isn't horrifically fragmented, that you
will be able to avoid needing to use one or more indirect blocks,
which will slightly speed up your filesystem and save a bit of space.

Simply moving to the ext4 filesystem will use a more advanced block
allocation system which can give some wins, although not as much as a
freshly formatted ext4 filesystem.

> Stability?

Note that to get full stability, you really want to be using either
the RHEL tech preview or Feodora 11 kernel and e2fsprogs (where Eric
has been very good about backporting the necessary stability fixes),
or 2.6.30 (once it is released) and e2fsprogs 1.41.6 (which was just
released).  We're fairly confident that ext4 has most of the scary
bugs worked out at this point, but keep in mind that for really
critical, production-critical enterprise systems, a paranoid sysadmin
might want to stick on ext3 for a while longer.  That being said, I've
used it on my laptop since last July, and haven't lost any data or
needed to resort to backups.  (Other people have turned up bugs, which
in a few cases have caused data loss, but that's why we all keep
regular backups, *RIGHT*?)

						- Ted