qm.adoc: rework clone/template sections

qm.adoc

@@ -522,12 +522,20 @@ Full Clone::
 The result of such copy is an independent VM. The
 new VM does not share any storage resources with the original.
 +
+
 It is possible to select a *Target Storage*, so one can use this to
 migrate a VM to a totally different storage. You can also change the
 disk image *Format* if the storage driver supports several formats.
 +
+
 NOTE: A full clone need to read and copy all VM image data. This is
 usually much slower than creating a linked clone.
++
+
+Some storage types allows to copy a specific *Snapshot*, which
+defaults to the 'current' VM data. This also means that the final copy
+never includes any additional snapshots from the original VM.
+
 
 Linked Clone::
 
@@ -536,33 +544,47 @@ clones. Such a clone is a writable copy whose initial contents are the
 same as the original data. Creating a linked clone is nearly
 instantaneous, and initially consumes no additional space.
 +
+
 They are called 'linked' because the new image still refers to the
 original. Unmodified data blocks are read from the original image, but
 modification are written (and afterwards read) from a new
 location. This technique is called 'Copy-on-write'.
 +
-This implies that the original is either a read-only 'snapshot', or a
-read-only 'Template' VM. It is not possible to change the *Target
-storage* for linked clones, because this is a storage internal
-feature.
+
+This requires that the original volume is read-only. With {pve} one
+can convert any VM into a read-only <<qm_templates, Template>>). Such
+templates can later be used to create linked clones efficiently.
 +
-NOTE: You cannot delete the original template or snapshot while
-linked clones exists.
+
+NOTE: You cannot delete the original template while linked clones
+exists.
++
+
+It is not possible to change the *Target storage* for linked clones,
+because this is a storage internal feature.
 
 
 The *Target node* option allows you to create the new VM on a
 different node. The only restriction is that the VM is on shared
 storage, and that storage is also available on the target node.
 
-It is possible to clone a specific *Snapshot*, which defaults to the
-'current' VM data. This also means that the final copy does not
-include any additional snapshots from the original VM.
-
 To avoid resource conflicts, all network interface MAC addresses gets
 randomized, and we generate a new 'UUID' for the VM BIOS (smbios1)
 setting.
 
 
+[[qm_templates]]
+Virtual Machine Templates
+-------------------------
+
+One can convert a VM into a Template. Such templates are read-only,
+and you can use them to create linked clones.
+
+NOTE: It is not possible to start templates, because this would modify
+the disk images. If you want to change the template, create a linked
+clone and modify that.
+
+
 Managing Virtual Machines with `qm`
 ------------------------------------