Is it safe to zpool upgrade my boot pool?

I have a home server that was originally installed with Ubuntu 14.04 and is currently running 19.10 (will eventually be upgraded to 20.04). All the filesystems, including the one that contains /boot, are ZFS. When I run zpool status rpool, it advises me to run zpool upgrade:

$ zpool status rpool pool: rpool 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 0 days 03:59:33 with 0 errors on Sun Jul 12 04:23:43 2020
config: NAME STATE READ WRITE CKSUM rpool ONLINE 0 0 0 raidz1-0 ONLINE 0 0 0 ata-WDC_WD10EZEX-00BN5A0_WD-WCC3F0ZX6U1R-part1 ONLINE 0 0 0 ata-WDC_WD10EZEX-00BN5A0_WD-WCC3F2VSJVE1-part1 ONLINE 0 0 0 ata-WDC_WD10EADS-11M2B1_WD-WCAV54517936-part1 ONLINE 0 0 0
errors: No known data errors

At the time I installed 14.04, I believe the advice was to explicitly disable certain ZFS features in order to make the pool readable to GRUB, which is why the above message is appearing in the first place. However, I have no idea if this advice still applies. Is it safe to run zpool upgrade rpool, or will doing so render my boot volume unreadable to GRUB and prevent it from booting?

Here are some hopefully relevant bits of system info:

$ apt-cache policy grub2 zfsutils-linux linux-image-generic
grub2: Installed: 2.04-1ubuntu12.2 Candidate: 2.04-1ubuntu12.2 Version table: *** 2.04-1ubuntu12.2 500 500 eoan-updates/universe amd64 Packages 100 /var/lib/dpkg/status 2.04-1ubuntu12 500 500 eoan/universe amd64 Packages
zfsutils-linux: Installed: 0.8.1-1ubuntu14.4 Candidate: 0.8.1-1ubuntu14.4 Version table: *** 0.8.1-1ubuntu14.4 500 500 eoan-updates/main amd64 Packages 100 /var/lib/dpkg/status 0.8.1-1ubuntu14 500 500 eoan/main amd64 Packages 500 eoan/main amd64 Packages
linux-image-generic: Installed: 5.3.0.62.52 Candidate: 5.3.0.62.52 Version table: *** 5.3.0.62.52 500 500 eoan-updates/main amd64 Packages 500 eoan-security/main amd64 Packages 100 /var/lib/dpkg/status 5.3.0.18.21 500 500 eoan/main amd64 Packages 500 eoan/main amd64 Packages
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 19.10
Release: 19.10
Codename: eoan
$ uname -a
Linux mneme.dedyn.io 5.3.0-62-generic #56-Ubuntu SMP Tue Jun 23 11:20:52 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

1 Answer

Given that I already have another computer running 20.04 on ZFS with all feature flags enabled, I decided to upgrade my server to 20.04 and then take the chance and run zpool upgrade (after verifying that both machines had the same versions of grub and zfs). It worked! My server still boots just fine. So while I can't say anything about 19.10, I can say that as of 20.04, running zpool upgrade on your boot pool should not render your machine unbootable.