svlug-journaling_file_systems_compared

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Date: Fri, 14 Dec 2001 11:00:04 -0500
From: Bryan-TheBS-Smith <b.j.smith@ieee.org>
To: Alexander Udalov <aludal@softhome.net>
Subject: Re: [svlug] Re: OFF TOPIC fsck for ext3

Alexander Udalov wrote:
> Thank you Drew, fsck did the fscking job (or was it actually
> fsck.ext3? hadn't the clue at the time, to check).

Ext3 uses the same, reliable fsck as Ext2, as their structures are
basically the same -- as long as your e2fsprogs package is up-to-date
for your Ext3 version, it knows how to handle the journal components.

Just for further note, on my RedHat 7.2 system, I did:
$ ls -la /sbin/fsck.ext*
  -rwxr-xr-x    3 root  root   561928 Aug 29 18:36 fsck.ext2
  -rwxr-xr-x    3 root  root   561928 Aug 29 18:36 fsck.ext3

A hard link???  Let's check:
$ ls -li fsck.ext*
  32927 -rwxr-xr-x    3 root     root       561928 Aug 29 18:36
fsck.ext2
  32927 -rwxr-xr-x    3 root     root       561928 Aug 29 18:36
fsck.ext3

Yep, inodes match.

> Well, fsck-ing was accomplished successfuly only in manual operation,
> so to speak, and with my unprintable curses about some losses of data
> discovered after the dust settled.

At least Ext3 is _paranoid_enough_ to say "hey, something happened, I
don't trust my journal."  Trust me, I'd rather have that _any_day_! 
I've been running Ext3 since early 2000 on dozens of workstations and
servers and it's nice to know that it uses Ext2's proven fsck, and its
not afraid to go to it if necessary.

After years of using HPFS and NTFS, it is obvious that IBM/Microsoft are
a little "too aggressive" in always going to the journal.  I've had 2 NT
Servers toast themselves in the past.  As such, I _force_ a full CHKDSK
everytime NT crashes -- which defeats the purpose of journaling in the
first place!  Several people have noted that IBM's JFS continues this
"aggressive" tradition as well.

I don't know about ReiserFS.  It seems that it actually knows when not
to trust its journal.  Unfortunately, in both cases where people I know
have had issues and dropped down to a full reiserfsck, they've
_completely_toasted_ their volume!  I guess good journaling means little
if the recovery tools are not mature enough -- I'm not saying ReiserFS
isn't, it just doesn't look that way.  Yeah, I'm sure that will net a
little flammage, but realize that ReiserFS is about features and
"pushing the envelope," whereas Ext3 benefits from Ext2's proven fsck
with little additional effort on the part of the Ext3 team.

And lastly, there is SGI's XFS.  I have been using it on over a dozen
Linux systems since February, and dozens of Irix systems since the
mid-90s.  XFS seems to be a filesystem that actively fixes and
defragments itself constantly, consistently and correctly.  On Linux,
provided I stick with the "releases" or be careful to use a good CVS tag
and configure/compile it correctly (and *NOT* with GCC 2.95/2.96!), I
haven't had any data loss yet.  The feature-set used to be unique, with
ACLs and official quota support, but even Ext3 has that now.  But there
is one small bonus I feel there is to using XFS, it seems (or at least
seemed to, at the time) _fix_ all the VM crap in the kernel -- because
XFS is integrated in the VM, and SGI tested the hell out of their
releases before putting the version stamp on them.

But those are just my opinions.

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