I am running a Ubuntu container in a snap lxd on a Ubuntu 20.04 LTS v-server.
I have a ZFS-based pool that reports just under 18 GiB space available:
$ lxc storage info default
info:
description: ""
driver: zfs
name: default
space used: 15.58GiB
total space: 17.92GiB
used by:
images:
- 9f7418d1db5ccfe14c775e8e2c54c694df28700eb99a9a8fe196a7f96e9411f0
instances:
- db-01
- wp-01
- ws-01
profiles:
- default
I have a container that reports ~15 GB total disk space:
$ df -h
Filesystem Size Used Avail Use% Mounted on
default/containers/ws-01 15G 12G 2.4G 84% /
none 492K 4.0K 488K 1% /dev
udev 1.9G 0 1.9G 0% /dev/tty
tmpfs 100K 0 100K 0% /dev/lxd
tmpfs 100K 0 100K 0% /dev/.lxd-mounts
tmpfs 2.0G 16K 2.0G 1% /dev/shm
tmpfs 394M 256K 393M 1% /run
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
snapfuse 64M 64M 0 100% /snap/core20/1623
snapfuse 44M 44M 0 100% /snap/certbot/2192
snapfuse 114M 114M 0 100% /snap/core/13425
snapfuse 62M 62M 0 100% /snap/core20/1611
snapfuse 115M 115M 0 100% /snap/core/13741
snapfuse 45M 45M 0 100% /snap/certbot/2344
tmpfs 394M 0 394M 0% /run/user/1001
To my great astonishment, I extracted an archive in this container which, when extracted, ballooned to a reported ~25GB in size:
65774 -rw-rw-r-- 1 stephen stephen 26470608214 Sep 3 09:28 data.sql
I expected this to cause disk full errors, but it has not. Why not? What is going on here?
Here is the storage pool information from zfs:
$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
default 15.6G 2.34G 24K none
default/containers 13.6G 2.34G 24K none
default/containers/db-01 796M 2.34G 1.11G none
default/containers/wp-01 847M 2.34G 1.03G none
default/containers/ws-01 12.0G 2.34G 11.7G none
default/custom 24K 2.34G 24K none
default/deleted 816M 2.34G 24K none
default/deleted/containers 24K 2.34G 24K none
default/deleted/custom 24K 2.34G 24K none
default/deleted/images 816M 2.34G 24K none
default/deleted/images/3dc53983cb37b781773e7dee3b651a24a306e6bff9facb2163970f9f3051c696 231M 2.34G 231M none
default/deleted/images/7e8bbf2f24234c9414314019cfa275870f945a6a2ed52c944c3c11a16a98e4ef 585M 2.34G 585M none
default/deleted/virtual-machines 24K 2.34G 24K none
default/images 1.19G 2.34G 24K none
default/images/9f7418d1db5ccfe14c775e8e2c54c694df28700eb99a9a8fe196a7f96e9411f0 1.19G 2.34G 1.19G none
default/virtual-machines 24K 2.34G 24K none