ZFS cache pool : incorrect size with df -h

[Keichi]

Hello,

 

On my unraid server, i have this cache pool :

 

It is 3x 1TB drives, with one mirror, for a total of 1.9 Tb useable capacity.

On the unraid console, when i do :

df -h

 

I have this output :

root@Yggdrasil:~# df -h
Filesystem                     Size  Used Avail Use% Mounted on
rootfs                          24G  1.6G   22G   7% /
tmpfs                           32M  2.2M   30M   7% /run
/dev/sda1                       58G  2.5G   55G   5% /boot
overlay                         24G  1.6G   22G   7% /lib
overlay                         24G  1.6G   22G   7% /usr
devtmpfs                       8.0M     0  8.0M   0% /dev
tmpfs                           24G     0   24G   0% /dev/shm
tmpfs                          128M  1.5M  127M   2% /var/log
tmpfs                          1.0M     0  1.0M   0% /mnt/disks
tmpfs                          1.0M     0  1.0M   0% /mnt/remotes
tmpfs                          1.0M     0  1.0M   0% /mnt/addons
tmpfs                          1.0M     0  1.0M   0% /mnt/rootshare
(array disks here)
cache                          939G   23G  916G   3% /mnt/cache
cache/system                   933G   17G  916G   2% /mnt/cache/system
cache/domains                  1.4T  417G  916G  32% /mnt/cache/domains
cache/appdata                  916G  2.3M  916G   1% /mnt/cache/appdata
cache/appdata/mosquitto        916G  256K  916G   1% /mnt/cache/appdata/mosquitto
cache/appdata/grafana          916G  1.3M  916G   1% /mnt/cache/appdata/grafana
cache/appdata/homeassistant    916G   93M  916G   1% /mnt/cache/appdata/homeassistant
cache/appdata/mysql            916G  119M  916G   1% /mnt/cache/appdata/mysql
cache/appdata/nginx            916G  1.0M  916G   1% /mnt/cache/appdata/nginx
(etc for others containers)

 

The "cache" is reported to be 939GB with only 23Gb used.

 

I dont really understand this value.

 

Is it because of ZFS ?

 

I use Glances (with Homepage), and i can't show the correct size of the cache pool :

 

It seems to be reported as the df command line.

 

Really not a big deal, but maybe i can use this to learn something more.

 

Thanks all,

 

K.

[JorgeB]

Because it's by dataset, look st the datasets and add them all, just domains dataset is using 417G, and note that those use GiB, GUI uses GB.

 

 

 

 

[Keichi]

Hello JorgeB,

 

Indeed, it is by dataset.

But why the main one (cache) did not report the full size of the pool array ?

It seems to only report one drive of the three.

 

That is more that i did not understand.

 

Maybe i could have done better configuring it ?

 

Thanks,

 

K.

[JorgeB]

Just now, Keichi said:

But why the main one (cache) did not report the full size of the pool array ?

Because as far as df can see there's no data there, data is inside the datasets, and datasets are separate zfs filesystems, for example if you try to move some data from one dataset to another a full copy will be done, instead of a move.

[Keichi]

Ok, i understand.

 

So it is impossible to report the full size of a ZFS cache pool, with the tool i use.

 

Thanks for the help, and as always, you clear answer.

 

K.

 

 

[JorgeB]

58 minutes ago, Keichi said:

So it is impossible to report the full size of a ZFS cache pool, with the tool i use.

BTW, if you need to get the used or free space from a zfs pool for a script or something, instead of df you can use:

 

zfs get -Hp -o value available,used <pool name>

 

[Keichi]

Thanks!

But, this is for Homepage (https://github.com/gethomepage/homepage) which uses Glances integration (https://github.com/nicolargo/glances).

 

I will ask directly on Glances' Github for more information.

 

I just wanted to understand better the issue and from you gave me, something is possible :

root@Yggdrasil:~# zfs get -Hp -o value available,used /mnt/cache
966035955456
963024068864

Values seem correct to me.

 

Thanks again JorgeB!

 

K.