du command doesn't give the right disk usage report

[ykchou99]

I use this command to create 100 20MBs files in a NFS share of TrueNAS.
# for i in {1..100}; do dd if=/dev/zero of=bigfile$i bs=1k count=20000; done
each file looks fine:
-rw-r--r--. 1 root root 20M Mar 27 16:10 bigfile1
But du command doesn't report correctly
# du -sh .
59K .

I also copy stuff from xfs to the share, but the TrueNAS share takes much smaller disk space vs. xfs

anyone else has the same issue? any suggestion ?

 

[Arwen]

This is expected behavior. TrueNAS uses ZFS, and ZFS can use compression. TrueNAS also likely enabled seamless, (and lossless), compression by default.

Thus, compressing "/dev/zero" output will compress VERY WELL. The 59KBs is just the directory entry data that describes the compressed data.

I suggest you read up on ZFS & TrueNAS. Their can be a few gotchas if missed following best practices.

 

[ykchou99]

thanks

 

[blanchet]

If you want to display the apparent size instead of the disk usage, then use du -A

Manpage: du(1)