[pve-devel] [PATCH docs] zfs: add section on zpool-features

[Stoiko Ivanov <s.ivanov@proxmox.com>]

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

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
---
 local-zfs.adoc | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/local-zfs.adoc b/local-zfs.adoc
index 4819678..a003a7c 100644
--- a/local-zfs.adoc
+++ b/local-zfs.adoc
@@ -699,3 +699,39 @@ 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 done between major version changes
+and are specified through *features*. All features and 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 actively done 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
+the new features.
+
+On the other hand there are a few downsides on enabling new features:
+
+* A system, with root on ZFS, still booting with `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 boot with an older kernel, which is still
+  shipping the old ZFS modules
+* Booting an older {pve} ISO to do repair a non-booting system likewise will not
+  work
+
+IMPORTANT: Do not upgrade your rpool if your system is still booted with `grub`.
+Systems installed before PVE 5.4, and systems booting with legacy boot (see
+xref:sysboot_determine_bootloader_used[how to determine the bootloader]), as
+this will render your system unbootable.
+
+.Enable new features for a pool:
+----
+# zpool upgrade <pool>
+----
+
-- 
2.20.1