ZFS binaries installed on the system? If it's the latter, the answer is you can't, not without breaking things probably and going against the ideology of TrueNAS being an appliance.
root@nas[~]# zpool status
pool: freenas-boot
state: ONLINE
status: Some supported features are not enabled on the pool. The pool can
still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
the pool may no longer be accessible by software that does not support
the features. See zpool-features(5) for details.
scan: scrub repaired 0B in 00:13:16 with 0 errors on Sun Jan 30 03:58:16 2022
config:
NAME STATE READ WRITE CKSUM
freenas-boot ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
da0p2 ONLINE 0 0 0
da1p2 ONLINE 0 0 0
errors: No known data errors
root@nas[~]# zpool upgrade
This system supports ZFS pool feature flags.
All pools are formatted using feature flags.
Some supported features are not enabled on the following pools. Once a
feature is enabled the pool may become incompatible with software
that does not support the feature. See zpool-features(5) for details.
POOL FEATURE
---------------
freenas-boot
multi_vdev_crash_dump
spacemap_histogram
enabled_txg
hole_birth
extensible_dataset
embedded_data
bookmarks
filesystem_limits
large_blocks
large_dnode
sha512
skein
userobj_accounting
encryption
project_quota
device_removal
obsolete_counts
zpool_checkpoint
spacemap_v2
allocation_classes
resilver_defer
bookmark_v2
redaction_bookmarks
redacted_datasets
bookmark_written
log_spacemap
livelist
device_rebuild
zstd_compress
root@nas[~]#
As I said before, it does not work.
* Depending on the exact featuref you do upgrade, you won't be able to roll back to a previous boot environment that doesn't natively have the feature flag set of the upgrade
Well, let's look at the various moving parts:For a while FreeNAS and latter on TrueNAS nagged you to upgrade the pool(s). Why?
zpool status
gain support for a "I want these feature flags, don't offer me any more" type of operation.zpool status
output and warn the user that new feature flags are available, but deciding not to warn the user tends to require either hacks (which are okay for something like a boot pool, which is a known quantity) or the sort of infrastructure that did not exist in ZFS and was never implemented on the FreeNAS/TrueNAS side of things.Could you please give some more technical details on why not to do it?First, all of the "how to" answers here are wrong--the way you should upgrade your pool is using the GUI. But the GUI doesn't allow doing that for the boot pool, and that's fine. Put more clearly, there's no reason at all to upgrade the ZFS feature flags for your boot pool. Don't do it, and don't worry about it.
I don't know that I can give technical details beyond what's already been shared--there's a non-zero risk that the FreeBSD loader won't boot from the pool with all the features enabled, and there's zero benefit to enabling them.Could you please give some more technical details on why not to do it?