ZFS USED twice as LUSED

[mailinglists]

Hi,

i noticed that my two of my backup VMs use internally less space than is seen on hipervizor.

Here is an example.
Inside VM:

/dev/sdb        4.0T  1.8T  2.2T  44% /backup

Outside VM:

rpool/data/vm-140-disk-1                                  2.70T  1.58T     2.70T  -
VOLSIZE  LUSED   USED  VOLBLOCK  COMPRESS  VOLBLOCK
  3.91T  1.66T  2.70T        8K        on        8K

Seems to me like the VM uses lots of small files (ext4 is default 4k) which in turn use 8k blocks on host and use twice as much disk space.
I might be wrong. It might also be related to compression. Does anyone care to explain?

I guess I could stop the VM, send rpool/data/vm-140-disk-1 elsewhere, recreate it (just this zvol) with 4k block size, send data back and start VM.
What do you guys think? Will this work and also decrease disk usage?

I also forgot why again we went with 8k default. I guess I could google.

 

[apoc]

What do you guys think?

I am using my magic crystal ball and can see you have a raidz based zfs pool
I also can see in there that the default ZVOL blocksize of 8k is used.

If that's wrong, my crystal ball needs re-calibration.

If it is true you need to create the zvol with a larger block size (64k, 128k) to avoid padding overhead.

 

[mailinglists]

Awesome reply.

 

[apoc]

Glad you did not pick up on it in a bad way because it just was supposed a little funny. We have those topics quite often recently. Forgot this link:
https://forum.proxmox.com/threads/u...reated-on-raidz3-pool-vs-mirrored-pool.65018/