No more free space after upgrading to 10.1 and zpool upgrade

[Olivier Cochard-Labbé]

Hi,

I've upgraded a small NAS to 10.1 and issue a zpool upgrade.
But now I've got a problem: my volume didn't have free space anymore (it
should have about 50GB of free space).

#zpool list storage
NAME      SIZE  ALLOC   FREE   FRAG  EXPANDSZ    CAP  DEDUP  HEALTH  ALTROOT
storage  9,06T  8,87T   198G    15%         -    97%  1.00x  ONLINE  -
# zfs list storage
NAME      USED  AVAIL  REFER  MOUNTPOINT
storage  7,09T      0   404M  /storage

=> notice the 0 in "AVAIL"

I've tried:
1. To export+import the pool but no change.
2. To delete about 20GB of files: no changes, still 0 free space available !

I didn't use snapshot too: Then I've got no snapshot nothing to delete.

What can I do for retrieving the free space ?

Thanks,

Olivier