Hey folks,
I have two questions about determining how much storage has been used
*inside* of an RBD.
First, I'm confused by the output of df. I've created, mapped, and
mounted a 500GB RBD, and see the following:
# df -h /srv/test
Filesystem Size Used Avail Use% Mounted on
/dev/rbd44 500G 7.5G 467G 2% /srv/test
# cd /srv/test
# du -sh .
20K .
Any ideas way a brand-new, no files added mount shows 7.5GB of used
space? Does this happen from the file system formatting (ext4 in this
case)?
Additionally, 500G - 7.5G != 467G (the number shown as Avail). Why
the huge discrepancy? I don't expect the numbers to add up exact due
to rounding from kB, MB, GB, etc, but they should be darn close, a la
df -h /dev/sda1
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 15G 1.7G 13G 12% /
Second question, is it possible to know how much storage has been used
in the RBD without mounting it and running df or du? For the same RBD
as above, I see:
# rbd info test
rbd image 'test'':
size 500 GB in 128000 objects
order 22 (4096 KB objects)
block_name_prefix: rb.0.18f9.2d9c66c6
parent: (pool -1)
Is there perhaps a way to know the number of objects that have been
'used'? Then I could take that and multiply by the object size (4MB).
I'm running 0.48.1argonaut on Ubuntu 12.04.
RBD maps are also on Ubuntu 12.04, with the stock 3.2.0-29-generic kernel.
Thanks,
- Travis
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