[RndTbl] "Missing" disk space

[Adam Thompson]

Documenting for posterity, and in case anyone else runs into the same
problem:


I ran into a situation today where df(1) showed me a filesystem that was
getting pretty full (109GB used out of 146GB), but when I used du(1) to
find the space hogs, it was only able to locate <30GB of data on the
partition.

(Hint: it was the root partition.)

The culprit turned out to be 87GB of files "hidden" underneath
mountpoints.  If you create /mnt/xyz, copy files into /mnt/xyz/*, then
mount another filesystem (local or remote) at /mnt/xyz, the original files
are still there, still taking up disk space, but unavailable.

Luckily, this was a Linux system, and I was able to get access to those
files using a rebind mount:
- mkdir /tmp/xyz"
- "mount -o rebind /dev/mapper/root_lv /tmp/xyz"
- "cd /tmp/xyz/mnt/xyz"
- "du -sh *"
...yup, there's 87GB of files that I *don't* see under /mnt/xyz.

It's pretty obvious that the files were intended to live on a remote
fileshare, but got copied in at a point in time when the remote filesystem
wasn't mounted.  Now I'm mv(1)'ing 87GB of data back across to a Windows
server across a CIFS mount... time to go for lunch, I guess!

[image: Avant logo] *Adam Thompson*
Senior Systems Administrator
*voice:* 204.789.9596 x24 | *email:* athompson at avant.ca | *web:* avant.ca
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.muug.mb.ca/pipermail/roundtable/attachments/20151222/66d27be7/attachment.html>