zfs snapshot_limit is not respected

[Gary Palmer]

On Thu, Feb 02, 2017 at 09:31:58PM -0500, Ultima wrote:
> I recently moved some data on a box with limited space. I decided I should
> limit the snapshots so that space would not become an issue. I just check
> back a week later to find out the box is hitting the borderline. Doing I
> quick check I realized that the snapshot_limit is not being respected.
> 
> # uname -a
> FreeBSD R1 11.0-STABLE FreeBSD 11.0-STABLE #17 r312232: Sun Jan 15 10:59:10
> EST 2017     root at S1:/usr/src/11-STABLE/obj/usr/src/11-STABLE/src/sys/MYKERNEL
>  amd64
> 
> # zfs create zroot/bhyve/test
> # zfs set snapshot_limit=0 zroot/bhyve/test
> # zfs snapshot zroot/bhyve/test at 1
> 
> 
> # zfs snapshot zroot/bhyve/test at 2
> # zfs snapshot zroot/bhyve/test at 3
> # zfs list -t snapshot | grep zroot/bhyve/test
> zroot/bhyve/test at 1                                           0      -
>  88K  -
> zroot/bhyve/test at 2                                           0      -
>  88K  -
> zroot/bhyve/test at 3                                           0      -
>  88K  -
> # zfs get all zroot/bhyve/test | grep snapshot
> zroot/bhyve/test  usedbysnapshots       0                      -
> zroot/bhyve/test  snapshot_limit        0                      local
> zroot/bhyve/test  snapshot_count        3                      local
> 
> Also wanted to verify 0 was not being mistaken for none.
> 
> # for snapshot in `zfs list -t snapshot | grep zroot/bhyve/test | awk
> '{print $1}'`; do zfs destroy $snapshot ; done
> 
> # zfs get all zroot/bhyve/test | grep snapshot
> zroot/bhyve/test  usedbysnapshots       0                      -
> zroot/bhyve/test  snapshot_limit        0                      local
> zroot/bhyve/test  snapshot_count        0                      local
> 
> # zfs set snapshot_limit=1 zroot/bhyve/test
> # zfs snapshot zroot/bhyve/test at 1
> # zfs snapshot zroot/bhyve/test at 2
> # zfs snapshot zroot/bhyve/test at 3
> # zfs get all zroot/bhyve/test | grep snapshot
> zroot/bhyve/test  usedbysnapshots       0                      -
> zroot/bhyve/test  snapshot_limit        1                      local
> zroot/bhyve/test  snapshot_count        3                      local
> 
> 
> Also tested on head
> FreeBSD S1 12.0-CURRENT FreeBSD 12.0-CURRENT #26 r312388: Wed Jan 18
> 12:38:52 EST 2017
> root at S1:/usr/src/head/obj/usr/src/head/src/sys/MYKERNEL-NODEBUG
>  amd64

Hi,

I suspect this line from the manpage is key:

The limit is not enforced if the user is allowed to change the limit

Regards,

Gary