[Lustre-discuss] free space of Lustre fs: unknown quantity?

[Thomas Roth]

Hi all,

on our test cluster I observe a rather large difference between "df" and
"lfs df":

> lfs df /lustre
> UUID 1K-blocks Used
Available Use% Mounted on
> ...
> filesystem summary: 137454163496 7056126648 130398036848
5% /lustre

vs.
> df /lustre
> Filesystem 1K-blocks Used
Available Use% Mounted on
> mds@tcp0:/lust1 137454163496 73850360 130398036848
1% /lustre

Using the human readable form, df -h, shows what this means: lfs
believes that 6.6TB are in use, while the system thinks it's only 71GB.
And of course, total and available space are equal.
I know that these tools for checking free and used disk space are
notoriously imprecise. Not surprisingly then, "du -hs /lustre" gives me
just 47 GB. I think I'd like to stick to "du" - gives best looking
results ;-)

So, any ideas on what goes wrong here? Does something go wrong at all?

Oh, btw, it is Lustre version 1.6.4.3 under Debian Etch 64 on this
system. And I can observe this behavior on several clients, also after
unmounting and remounting.

Regards,
Thomas
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[Andreas Dilger]

On May 07, 2008 17:57 +0200, Thomas Roth wrote:
> on our test cluster I observe a rather large difference between "df" and
> "lfs df":
>
> > lfs df /lustre
> > UUID 1K-blocks Used
> Available Use% Mounted on
> > ...
> > filesystem summary: 137454163496 7056126648 130398036848
> 5% /lustre
>
> vs.
> > df /lustre
> > Filesystem 1K-blocks Used
> Available Use% Mounted on
> > mds@tcp0:/lust1 137454163496 73850360 130398036848
> 1% /lustre
>
> Using the human readable form, df -h, shows what this means: lfs
> believes that 6.6TB are in use, while the system thinks it's only 71GB.
> And of course, total and available space are equal.
> I know that these tools for checking free and used disk space are
> notoriously imprecise. Not surprisingly then, "du -hs /lustre" gives me
> just 47 GB. I think I'd like to stick to "du" - gives best looking
> results ;-)
>
> So, any ideas on what goes wrong here? Does something go wrong at all?

This is bug 14283, and is fixed in 1.6.5. The problem is described best at:

https://bugzilla.lustre.org/show_bug.cgi?id=14283#c2

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.