[pve-devel] [PATCH docs] Add warning about using qcow2 images on a ZFS filesystem

[Emmanuel Kasper]

---
 local-zfs.adoc | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/local-zfs.adoc b/local-zfs.adoc
index 9b682b9..1b9f682 100644
--- a/local-zfs.adoc
+++ b/local-zfs.adoc
@@ -254,6 +254,22 @@ can be used as cache.
 
  zpool replace -f <pool> <old device> <new-device>
 
+Using a directory storage on top of ZFS filesystem
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you add a directory storage on top of a ZFS filesystem, VM disks in this
+storage will be stored in the `qcow2` or `raw` format, and you will have two
+layers of file systems. This can reduce the performance, especially if you
+choose the `qcow2` format, because then you will have a "copy on write" disk
+image that writes on a "copy on write" file system (ZFS). So we usually
+recommend creating an additional ZFS subvolume in the pool, and to use this
+subvolume as {pve} storage, to keep the ZFS benefits of snapshots and
+checksumming. For example we create here the `vms_subvolume` in the `rpool`
+pool.
+
+ zfs create rpool/vms_subvolume
+
+Then add the newly created subvolume via the command line or GUI.
 
 Activate E-Mail Notification
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -275,7 +291,6 @@ configured for the root user.
 IMPORTANT: The only setting that is required is `ZED_EMAIL_ADDR`. All
 other settings are optional.
 
-
 Limit ZFS Memory Usage
 ~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.1.4