[pve-devel] [PATCH pve-docs v3] fix #5644: Split the section on creating a swap partition on a ZVol.

[Alexander Abraham]

The section "SWAP on ZFS" was split into two parts. The first part
contains general instructions on how to create a swap partition and
how to set the level of "swappiness". The second part contains a
warning about creating a swap partition on a ZFS volume.The official
ZFS documentation, which has been linked in a footnote, explains
that creating a swap partition on a ZFS volume could lead to
dangerous and undefined behavior.

Signed-off-by: Alexander Abraham <a.abraham at proxmox.com>
---
 local-zfs.adoc | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/local-zfs.adoc b/local-zfs.adoc
index c64fb27..d411222 100644
--- a/local-zfs.adoc
+++ b/local-zfs.adoc
@@ -622,14 +622,9 @@ time this value changes:
 You *must reboot* to activate these changes.
 ====
 
-
-[[zfs_swap]]
-SWAP on ZFS
-~~~~~~~~~~~
-
-Swap-space created on a zvol may generate some troubles, like blocking the
-server or generating a high IO load, often seen when starting a Backup
-to an external Storage.
+[[creating_swap_partitions]]
+Creating SWAP Partitions
+~~~~~~~~~~~~~~~~~~~~~~~~
 
 We strongly recommend to use enough memory, so that you normally do not
 run into low memory situations. Should you need or want to add swap, it is
@@ -637,18 +632,18 @@ preferred to create a partition on a physical disk and use it as a swap device.
 You can leave some space free for this purpose in the advanced options of the
 installer. Additionally, you can lower the
 ``swappiness'' value. A good value for servers is 10:
-
+ 
 ----
 # sysctl -w vm.swappiness=10
 ----
-
+ 
 To make the swappiness persistent, open `/etc/sysctl.conf` with
 an editor of your choice and add the following line:
 
 --------
 vm.swappiness = 10
 --------
-
+ 
 .Linux kernel `swappiness` parameter values
 [width="100%",cols="<m,2d",options="header"]
 |===========================================================
@@ -663,6 +658,15 @@ improve performance when sufficient memory exists in a system.
 | vm.swappiness = 100 | The kernel will swap aggressively.
 |===========================================================
 
+[[zfs_swap]]
+SWAP on ZFS
+~~~~~~~~~~~
+
+It is strongly recommended to not use a ZFS volume for creating a swap partition
+because this could lead to deadlocks. These deadlocks could cause the affected 
+system to freeze. The OpenZFS documentation footnote:[https://openzfs.github.io/openzfs-docs/Project%20and%20Community/FAQ.html#using-a-zvol-for-a-swap-device-on-linux]
+warns about using a ZFS volume for creating a swap partition.
+
 [[zfs_encryption]]
 Encrypted ZFS Datasets
 ~~~~~~~~~~~~~~~~~~~~~~
-- 
2.39.5