[Jfs-discussion] Re: directory access time for jfs vs. ext3

[Dave K. <sh...@au...>]

On Fri, 2004-06-11 at 11:24, Yaron Minsky wrote:
> On Wed, 2004-06-09 at 14:20, Dave Kleikamp wrote:
> > On Wed, 2004-06-09 at 11:17, Charles Floyd wrote:
> > >
> > > [11:13:21 cfloyd@frontend-0 2004-01-02]$ time ls -1 | wc -l
> >
> > 'ls -l' not only reads the directory, but reads the inode for each entry
> > in order to get the file-type, size, modification times, etc.
> 
> That's actually not -l (the letter l), but rather -1 (the number 1).
> i.e., it was listed in single-column mode, to ensure that the number of
> lines was equal to the number of files.

Oops.  It's hard to tell the difference in the font I'm using.  :^)

> Even then, though, the difference in performance seems pretty huge ---
> almost two orders of magnitude.  Are 2-second ls times normal for a
> large JFS directory?  I thought JFS was supposed to beat ext3 on large
> directories in particular.

I'm not sure what the reason for the difference is.  I don't think there
is an expectation that jfs would enumerate a directory faster than ext3,
as you need to read both directories in their entirety.  I would expect
jfs to lookup a particular entry faster than ext3.  Of course,
benchmarking a path lookup may be difficult, because you would have to
make sure the entry was not cached in the dcache. 
-- 
David Kleikamp
IBM Linux Technology Center