Question About Available Space

[Alan Smithee]

FreeNAS-9.3-STABLE-201502232343

I have 4x3TB drives running RaidZ2 (or I hope it is)

Code:

pool: tank
state: ONLINE
  scan: scrub repaired 0 in 2h58m with 0 errors on Thu Mar  5 11:31:47 2015
config:

        NAME                                            STATE     READ WRITE CKSUM
        tank                                            ONLINE       0     0     0
          raidz2-0                                      ONLINE       0     0     0
            gptid/7a57241a-bdec-11e4-9005-ac9e17e0a1f4  ONLINE       0     0     0
            gptid/7b02a3a0-bdec-11e4-9005-ac9e17e0a1f4  ONLINE       0     0     0
            gptid/7bad308d-bdec-11e4-9005-ac9e17e0a1f4  ONLINE       0     0     0
            gptid/7c6fc077-bdec-11e4-9005-ac9e17e0a1f4  ONLINE       0     0     0

errors: No known data errors

I thought I would get somewhere around 5-6TB of free space (2 main, 2 parity drives), but for some reason the free space (on df -h and the web interface) reports around 3.3TB.

Code:

Filesystem                                              Size    Used   Avail Capacity  Mounted on
freenas-boot/ROOT/FreeNAS-9.3-STABLE-201502232343        13G    943M     12G     7%    /
devfs                                                   1.0k    1.0k      0B   100%    /dev
tmpfs                                                    32M    5.3M     26M    17%    /etc
tmpfs                                                   4.0M    8.0k      4M     0%    /mnt
tmpfs                                                   5.2G     16M    5.2G     0%    /var
freenas-boot/grub                                        12G    7.8M     12G     0%    /boot/grub
tank                                                    3.3T    151k    3.3T     0%    /mnt/tank
tank/media                                              4.3T      1T    3.3T    23%    /mnt/tank/media

Is that normal overhead or did I mis-configure something?

Also, I'm a little confused as I have a dataset (media) that is larger in size (in df -h) than what the web interface seems to be reporting.

 

[Bidule0hm]

"I hope it is" Yes, it is ;)

The difference is because the size of a dataset is equal to the total size minus the space used on the other datasets in the same pool.

As you can see you have tank/media wich is 4.3 TiB in size and there is 1 TiB of data on it so the available space is 3.3 TiB.

The difference between the expected 5-6 and real 4.3 TiB is because of the TB/TiB conversion and the metedata overhead (checksums, ACLs, ...).

 

[Alan Smithee]

Thanks for your reply (and for the calculator).

And for those with a similar question, here is some help : https://forums.freenas.org/index.php?threads/zfs-raid-size-calculator.28191/

 

[Bidule0hm]

You're welcome ;)

But if you can edit to link to the thread instead of the app directly it would be great because if I change something on the app the link will change, thanks.

 

[cyberjock]

Also you should *never* use df or du for ZFS. It doesn't actually understand ZFS correctly.