Large discrepancy in reported disk usage on USR partition

[Jeremy Chadwick]

On Thu, Oct 30, 2008 at 12:11:58PM +1030, Brendan Hart wrote:
> The space reserved as minfree does not appear to have been changed from the
> default setting of 8%.

Okay, then that's likely not the problem.

> Is your suggestion that I should change it to a larger value?

That would just make your problem worse.  :-)

> I don't understand how modifying it now could fix the situation, but I
> could be missing something.

Well, the feature I described isn't what's causing your problem, but to
clarify: if you change the percentage, it applies immediately.  I read
"I don't understand how modifying it now could fix ..." to mean "isn't
this option applied during newfs?"

> I have not observed the problem on any of the other ~dozen FreeBSD servers
> in our data centre. 

Unless someone more clueful chimes in with better hints, the obvious
choice here is going to be "recreate the filesystem".  I'd tell you
something like "try using ffsinfo(8)?", but I've never used the tool,
so very little of the output will make sense to me.

> Could the "missing" space be an indication of hardware disk issues i.e.
> physical blocks marked as bad? 

The simple answer is no, bad blocks would not cause what you're seeing.
smartctl -a /dev/disk will help you determine if there's evidence the
disk is in bad shape.  I can help you with reading SMART stats if need
be.

Since you booted single-user and presumably ran fsck -f /usr, and
nothing came back, I'm left to believe this isn't filesystem corruption.

> Is it possible on UFS2 for disk space to be allocated but hidden somehow?
> (although I have been running the commands such as "du -x" as superuser)

That's exactly what the above tunefs parameter describes.

> Similarly, is it possible on UFS2 for disk space to be allocated in "lost
> cluster chains" ?

I don't know what this means.  Someone more clueful will have to answer.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |