Re: [List] Cannot find out what uses space in ZFS dataset

> On 19 Sep 2025, at 09:22, Andrea Venturoli <ml@netfence.it> wrote:
> 
> On 9/18/25 21:50, freebsd@vanderzwan.org wrote:
> 
>> One thing that could explain this difference between du and zfs used is if you mount a small/empty filesystem on top of a very large directory.
> > In that case the content of the directory would be invisible because the mount masks it.
> 
> Doh!
> I hadn't thought about this! That's quite obvious and it even happened to me a few times in the past!
> 
> Following a suggestion on a forum, I tried:
>> mkdir /mnt/test
>> mount -t nullfs / /mnt/test
> but what I see under /mnt/test is identical to what I see under /.
> 
> The suggestion above was for UFS. I guess it works with ZFS too. Doesn't it?
> 
> 
Yes it's the way mounts work independent of the filesystem type ( except I guess for unionfs ).


> 
>> Does the output of the mount command show any strange mounts that could cause this ?
> 
> Nothing.
> 
Strange. I'm afraid that was the last thing I could think of.

> 
> 
>> About the du output what does ‘du -mx / |sort -n |tail ‘ show ?
> 
>> # du -mx / |sort -n |tail
>> 238     /usr/local/lib/python3.11
>> 442     /usr/lib/debug/boot
>> 539     /usr/local/lib
>> 567     /usr/lib/debug/usr/bin
>> 758     /usr/lib/debug/usr
>> 1229    /usr/local
>> 1235    /usr/lib/debug
>> 1371    /usr/lib
>> 3051    /usr
>> 3394    /
> 
> That's coherent with my earlier du output.
> 

Agree. So that leaves us the mystery why zfs says the dataset is using 60GB ;-(
With what we know now I have no idea why.


Cheers,
	Paul