ZFS doesn't update free space correctly

[sandman]

Hello

I've been having a problem with a thin-provisioned filesystem on ZFS. Right now I'm not really sure if its a problem with proxmox or the guest. Right now my setup is:

ZFS:

NAME                       USED  AVAIL  REFER  MOUNTPOINT
rpool                     10.2T  47.1G   140K  /rpool
rpool/ROOT                45.0G  47.1G   140K  /rpool/ROOT
rpool/ROOT/pve-1          35.0G  57.0G  35.0G  /
rpool/data                10.1T  47.1G   140K  /rpool/data
rpool/data/vm-100-disk-2  10.1T  47.1G  10.1T  -
rpool/swap                8.50G  53.4G  2.19G  -

Guest:
- Running Debian 8.10
- Over provisioned disk (10035G, shows as 9.8TiB)
- Disk is mounted as scsi-virtio with discard option marked on proxmox.
- Free space on disk:

# df  -h /u
S.ficheros     Tamaño Usados  Disp Uso% Montado en
/dev/sda         9,8T   6,9T  2,4T  75% /u

- Output of fstrim

# fstrim -v /u
/u: 27,6 GiB (29595009024 bytes) trimmed

You can see there is a pretty huge difference between free space on the guest and what ZFS is showing. I have a small reservation on rpool/ROOT/pve-1 to make sure it doesn't completely fills root.

Is there any way to correctly reclaim the free space on the guest?

 

[dcsapak]

do you have snapshots on that disk? do you have checked the box 'thin-provisioned' ? if not, marks the disk as not sparse and it uses the specified space

 

[sandman]

- No snapshots at all.
- Thin provision is enabled on ZFS storage


- How would I mark the disk as not sparse? Just uncheck discard on the disk?

EDIT:
So when doing a zfs get all I noticed this:

# zfs get all rpool/data/vm-100-disk-2
NAME                      PROPERTY              VALUE                  SOURCE
rpool/data/vm-100-disk-2  type                  volume                 -
rpool/data/vm-100-disk-2  creation              Mon Jul 10 10:45 2017  -
rpool/data/vm-100-disk-2  used                  10.1T                  -
rpool/data/vm-100-disk-2  available             47.1G                  -
rpool/data/vm-100-disk-2  referenced            10.1T                  -
rpool/data/vm-100-disk-2  compressratio         1.00x                  -
rpool/data/vm-100-disk-2  reservation           none                   default
rpool/data/vm-100-disk-2  volsize               9.80T                  local
rpool/data/vm-100-disk-2  volblocksize          8K                     default
rpool/data/vm-100-disk-2  checksum              on                     default
rpool/data/vm-100-disk-2  compression           on                     inherited from rpool
rpool/data/vm-100-disk-2  readonly              off                    default
rpool/data/vm-100-disk-2  createtxg             1811                   -
rpool/data/vm-100-disk-2  copies                1                      default
rpool/data/vm-100-disk-2  refreservation        none                   default
rpool/data/vm-100-disk-2  guid                  9301506174573547132    -
rpool/data/vm-100-disk-2  primarycache          all                    default
rpool/data/vm-100-disk-2  secondarycache        all                    default
rpool/data/vm-100-disk-2  usedbysnapshots       0B                     -
rpool/data/vm-100-disk-2  usedbydataset         10.1T                  -
rpool/data/vm-100-disk-2  usedbychildren        0B                     -
rpool/data/vm-100-disk-2  usedbyrefreservation  0B                     -
rpool/data/vm-100-disk-2  logbias               latency                default
rpool/data/vm-100-disk-2  dedup                 off                    default
rpool/data/vm-100-disk-2  mlslabel              none                   default
rpool/data/vm-100-disk-2  sync                  standard               inherited from rpool
rpool/data/vm-100-disk-2  refcompressratio      1.00x                  -
rpool/data/vm-100-disk-2  written               10.1T                  -
rpool/data/vm-100-disk-2  logicalused           6.93T                  -
rpool/data/vm-100-disk-2  logicalreferenced     6.93T                  -
rpool/data/vm-100-disk-2  volmode               default                default
rpool/data/vm-100-disk-2  snapshot_limit        none                   default
rpool/data/vm-100-disk-2  snapshot_count        none                   default
rpool/data/vm-100-disk-2  snapdev               hidden                 default
rpool/data/vm-100-disk-2  context               none                   default
rpool/data/vm-100-disk-2  fscontext             none                   default
rpool/data/vm-100-disk-2  defcontext            none                   default
rpool/data/vm-100-disk-2  rootcontext           none                   default
rpool/data/vm-100-disk-2  redundant_metadata    all                    default

logicalused and logicalreferenced show the right space used.