How can one reliably measure filesystem usage on partitions that were
compiled with -m reflink=1 ?
Here are some numbers i am measuring with df -h (on different partitions
holding the same data):
7.7G of 36G (-b size=512 -m crc=0 )
8.6G of 36G (-b size=4096 -m crc=1 )
11G of 36G (-b size=1024 -m crc=1,reflink=1,rmapbt=1 -i sparse=1 )
32G of 864G (-b size=4096 -m crc=1,reflink=1 )
I already ruled out fragmentation as a cause. The data does not contain
many duplicates (roughly 200mb could be freed by deduplicating). Since
measuring fs usage on btrfs also isn't trivial, i would suspect that
there are similar problems happening here. But i could not find any
information on how to measure fs usage properly when using xfs with
reflinks. Kernel in use is 4.14.40.
Tarik Ceylan
(I am not subscribed to this list, i'd be grateful if you could CC me in
your reply)
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