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zfs: add section on zpool-features

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primarily in order to warn users booting from ZFS with grub.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Reviewed-By: Aaron Lauterer <a.lauterer@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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Stoiko Ivanov 2021-03-31 11:52:04 +02:00 committed by Thomas Lamprecht
parent 6755848905
commit 18d0d68e4e
1 changed files with 35 additions and 0 deletions
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local-zfs.adoc
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@ -699,3 +699,38 @@ in the pool will opt in for small file blocks).
----
# zfs set special_small_blocks=0 <pool>/<filesystem>
----
[[sysadmin_zfs_features]]
ZFS Pool Features
~~~~~~~~~~~~~~~~~
Changes to the on-disk format in ZFS are only made between major version changes
and are specified through *features*. All features, as well as the general
mechanism are well documented in the `zpool-features(5)` manpage.
Since enabling new features can render a pool not importable by an older version
of ZFS, this needs to be done actively by the administrator, by running
`zpool upgrade` on the pool (see the `zpool-upgrade(8)` manpage).
Unless you need to use one of the new features, there is no upside to enabling
them.
In fact, there are some downsides to enabling new features:
* A system with root on ZFS, that still boots using `grub` will become
unbootable if a new feature is active on the rpool, due to the incompatible
implementation of ZFS in grub.
* The system will not be able to import any upgraded pool when booted with an
older kernel, which still ships with the old ZFS modules.
* Booting an older {pve} ISO to repair a non-booting system will likewise not
work.
IMPORTANT: Do not upgrade your rpool if your system is still booted with `grub`,
as this will render your system unbootable. This includes systems installed
before {pve} 5.4, and systems booting with legacy BIOS boot (see
xref:sysboot_determine_bootloader_used[how to determine the bootloader]).
.Enable new features for a pool:
----
# zpool upgrade <pool>
----