Rsync or untar hangs during operation

Hi everybody!
I tried find sth about it but I didn’t .
While I’m rsyncing data to lxd container or untar tgz on lxd - these operations hangs for minutes or hours.
I think that I have trouble with zfs storage, but I can’t find too many errors or warnings.
What to do?
I’m using Ubuntu 16.04 64-bits and lxd from snap
I updated lxd from apt to snap and loose ma container but I created new one - maybe I did sth wrong and I should repeated from beggining?

Extremely long waits could be explained by you running out of diskspace, ZFS will hold all write operations indefinitely when the device it’s using (quite likely a loop file in your case) is full.

I think there is enough space …
Maybe zfs has a problem with allocating new space on file-disk? There is a lot of spl_system_task processes

Filesystem      Size  Used Avail Use% Mounted on
udev             32G  148K   32G   1% /dev
tmpfs           6.3G  691M  5.6G  11% /run
/dev/sda3       1.8T  1.4T  383G  78% /
tmpfs            32G   96K   32G   1% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs            32G     0   32G   0% /sys/fs/cgroup
tmpfs           6.3G     0  6.3G   0% /run/user/0
tmpfs           6.3G   12K  6.3G   1% /run/user/127
tmpfs           6.3G     0  6.3G   0% /run/user/3031
tmpfs           6.3G     0  6.3G   0% /run/user/3247
/dev/loop0       82M   82M     0 100% /snap/core/4206
/dev/loop2       48M   48M     0 100% /snap/lxd/5866

zpool list
lxd   99,5G  29,5G  70,0G         -    23%    29%  1.00x  ONLINE  -

zfs list
NAME                                                                          USED  AVAIL  REFER  MOUNTPOINT
lxd                                                                          29,5G  66,9G    19K  none
lxd/containers                                                               24,8G  66,9G    19K  none
lxd/containers/hmtest-00                                4,45G  66,9G  8,95G  /var/snap/lxd/common/lxd/storage-pools/lxd/containers/hmtest-00
lxd/containers/hmtest-72                                20,4G  66,9G  24,8G  /var/snap/lxd/common/lxd/storage-pools/lxd/containers/hmtest-72
lxd/custom                                                                     19K  66,9G    19K  none
lxd/deleted                                                                    19K  66,9G    19K  none
lxd/images                                                                   4,71G  66,9G    19K  none
lxd/images/f71e76edd33548e6c898fad9778997f84d494ad779761ce34826c41031c151fc  4,71G  66,9G  4,71G  none
lxd/snapshots                                                                  19K  66,9G    19K  none

ls /var/snap/lxd/common/lxd/disks/ -lh
total 56G
drwx------  2 root root 4.0K Mar 26 13:46 .
drwx--x--x 14 root root 4.0K Mar 27 17:49 ..
-rw-------  1 root root 100G Mar 28 11:55 lxd.img

du -h /var/snap/lxd/common/lxd/disks/ 
56G	/var/snap/lxd/common/lxd/disks/

I’ve restarted host server and copying data was succesful! No more hangs.
I think I messed up with update-ing Ubuntu and lxd

Thanks Stéphane for quick reply and help!