FC5: "ext_attr" and "large_file" features for ext3 file systems ???

[Andreas Dilger]

On Apr 03, 2006  19:03 -0700, Robinson Tiemuqinke wrote:
>  Do I have to run "e2fsck -y -D" on a file system to
> active "dir_index" feature? 

You do not HAVE to run this, as new directories and existing directories
that grow larger than one block (normally 4kB) will start to use the
directory indexing feature.  However, to use dir indexing on existing
large directories you do need to use "e2fsck -f -D".  This will also
"pack" large directories that have had most of the files deleted out,
AFAIR.

>  I have bunches of old ext3 file systems created with
> old versions of mkfs.ext3, then after upgraded to
> Fedora Core 5, I run "tune2fs -O dir_index" to have
> turned on the feature, but it is rumored that I have
> to run "e2fsck -y -D" after unmounting old ext3 file
> systems so that new file and directory creations will
> use hased B-tree. 
> 
>  If that's corrct? If I don't run "e2fsck -y -D", then
> original linear directory structure will be still in
> effect even I turned on "dir_index" feature with
> tune2fs? For this case, what's the potential effects
> on the underlying old ext3 file systems?
> 
> Thanks a lot.
>  
> 
>  
> --- "Stephen C. Tweedie" <sct at redhat.com> wrote:
> 
> > Hi,
> > 
> > On Tue, 2006-03-28 at 13:52 -0800, Robinson
> > Tiemuqinke wrote:
> > 
> > >  First, what's the "large_file" feature REALLY
> > means?
> > > Then, what's the size of "large file" to light
> > this
> > > feature on? 2GB, or 2TB? 
> > 
> > 2GB.
> > 
> > >  Second, the "ext_attr" feature seems another
> > > automatic one: it only appears after the first
> > > "setfacl" command runs on the file system and then
> > the
> > > feature will keep on there forever even ACL is
> > > removed. What's the indication of "ext_attr"
> > feature
> > > and what are the reasons behind to have this
> > feature?
> > 
> > They are there simply to indicate that a given
> > feature is present on the
> > filesystem.  They prevent old versions of the kernel
> > and/or e2fsck tools
> > from mistakenly operating on a filesystem with newer
> > features,
> > potentially corrupting things on disk or returning
> > incorrect file
> > contents.
> > 
> > All remotely recent kernels have large file support
> > for ext3, and all
> > 2.6 ones (and many vendor-supplied 2.4 ones) have
> > ext_attr, so you have
> > to be running something pretty old to run into
> > compatibility problems
> > with either of those features.
> > 
> > --Stephen
> > 
> > 
> > 
> 
> 
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Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.