Reiserfs vs ext3

[Karl Hegbloom]

On Tue, 2005-03-08 at 10:54 -0500, Matthew S-H wrote:
> What are the differences between reiserfs and ext3?  Like, what are the 
> advantages and disadvantages?

Reiserfs uses a btree (IIRC) structure to organize the directory (and
data?), so it's a lot faster to find a particular file in a directory
with many files in it --- O(log(n)), vs O(n).  It also has a way of
compacting some of the data.  A very small file can be put on the same
block as the inode, saving a seek and read.  (or was that XFS?)  It also
can combine file 'tails' on single blocks.  The last part of a file,
that does not fill an entire block, can be placed on a block shared by
the tail of another file.  This saves disk space and can cut down on
reads from the hard drive in the case where both files are needed at
once --- eg. compilation.

XFS is also very good.  It has many of the advantages of Reiserfs, and
may be more stable.  It works well for a server, but use an
interruptible power supply.  I found it does not like to be 'switched
off' without an orderly shutdown.  (ext3 has data journalling as well as
meta-data journalling.  XFS has only meta-data journalling, afaik.)  You
cannot 'xfs_repair' it while it's mounted, so that must be done from
rescue media or an extended initrd.  XFS is very reliable and fast.

This is all from memory, learned by reading "Linux File Systems", by
Moshe Bar (author of "Linux Internals"), Osbourne / McGraw Hill, 2001,
ISBN 0-07-212955-7.  I do not claim to be an expert, and you should take
my statements above as potentially incorrect (or more like "not quite
exactly correct?" ;-)

> Its too late for me to reformat (probably not worth it anyway), but it 
> would be nice to know for future Ubuntu setups.

Don't do it without a full backup... there's a tool called 'convertfs'
that can change a file system from one type to another in place.  I've
successfully used it a number of times, but at least once it failed and
I needed the backup.  I don't think you can convert / (or any mounted
file system ?) without booting from rescue media.