ZFS: destroying snapshots without compromising boot environments

[Graham Perrin]

On 28/03/2020 15:19, Allan Jude wrote:

 > You can try to destroy the snapshot, if it is the basis of a clone, then
 > you will get an error, that you'd need to destroy the BE first, so you
 > might decide to keep that snapshot. As long as you don't use the -R flag
 > to zfs destroy dataset at snapshot, it will not destroy the clones.
 >
 > You can also use 'zfs promote' to make the clone into the parent, making
 > the original parent into the clone. This allows you to destroy that
 > original and the snapshot while keeping the clone.

Perfect, thank you. I was nervous about destruction without warning.

Below, are the differences (in measurement) between beadm and bectl to 
be expected?

----

root at momh167-gjp4-8570p:~ # beadm list
BE       Active Mountpoint  Space Created
Waterfox -      -           15.9G 2020-03-10 18:24
r357746f -      -            1.3G 2020-03-20 06:19
r359249b NR     /           74.7G 2020-03-28 01:19
root at momh167-gjp4-8570p:~ # beadm list -aDs
BE/Dataset/Snapshot                            Active Mountpoint Space 
Created

Waterfox
   copperbowl/ROOT/Waterfox                     -      - 137.0M 
2020-03-10 18:24
     r359249b at 2020-03-17-21:57:17               -      - 59.2G 
2020-03-17 21:57
   copperbowl/ROOT/Waterfox at 2020-03-20-06:19:45 -      - 67.0M 
2020-03-20 06:19

r357746f
   copperbowl/ROOT/r357746f                     -      - 1.2G 2020-03-20 
06:19
     Waterfox at 2020-03-20-06:19:45               -      - 59.2G 
2020-03-20 06:19

r359249b
   copperbowl/ROOT/r359249b at 2020-03-17-21:57:17 -      - 15.7G 
2020-03-17 21:57
   copperbowl/ROOT/r359249b                     NR     / 59.0G 
2020-03-28 01:19
root at momh167-gjp4-8570p:~ # bectl list
BE       Active Mountpoint Space Created
Waterfox -      -          204M  2020-03-10 18:24
r357746f -      -          1.21G 2020-03-20 06:19
r359249b NR     /          74.7G 2020-03-28 01:19
root at momh167-gjp4-8570p:~ # bectl list -aDs
BE/Dataset/Snapshot                              Active Mountpoint Space 
Created

Waterfox
   copperbowl/ROOT/Waterfox                       -      - 204M  
2020-03-10 18:24
   Waterfox at 2020-03-20-06:19:45                   -      - 67.0M 
2020-03-20 06:19

r357746f
   copperbowl/ROOT/r357746f                       -      - 1.21G 
2020-03-20 06:19

r359249b
   copperbowl/ROOT/r359249b                       NR     / 74.7G 
2020-03-28 01:19
   r359249b at 2020-03-17-21:57:17                   -      - 15.7G 
2020-03-17 21:57
root at momh167-gjp4-8570p:~ # zfs list -t snapshot
NAME                                                     USED AVAIL  
REFER  MOUNTPOINT
copperbowl/ROOT/Waterfox at 2020-03-20-06:19:45            67.0M -  59.2G  -
copperbowl/ROOT/r359249b at 2020-03-17-21:57:17            15.7G -  59.2G  -
copperbowl/iocage/releases/12.0-RELEASE/root at jbrowsers     8K -  1.24G  -
copperbowl/poudriere/jails/head at clean                    328K -  1.89G  -
root at momh167-gjp4-8570p:~ # zfs destroy 
copperbowl/ROOT/r359249b at 2020-03-17-21:57:17
cannot destroy 'copperbowl/ROOT/r359249b at 2020-03-17-21:57:17': snapshot 
has dependent clones
use '-R' to destroy the following datasets:
copperbowl/ROOT/r357746f
copperbowl/ROOT/Waterfox at 2020-03-20-06:19:45
copperbowl/ROOT/Waterfox
root at momh167-gjp4-8570p:~ # date ; uname -v
Sat Mar 28 15:30:57 GMT 2020
FreeBSD 13.0-CURRENT #1 r359249: Tue Mar 24 00:12:27 GMT 2020 
root at momh167-gjp4-8570p:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG
root at momh167-gjp4-8570p:~ #