buildsys: don't use rm -r on so many globs

[pve-docs.git] / qm.adoc

diff --git a/qm.adoc b/qm.adoc
index c1d79b9e4d5ef839fa214e9e9d6ef6fbe65a8a5d..ed2ab8d5d4231b5689a785bb4f26f20dddc16ad7 100644 (file)
--- a/qm.adoc
+++ b/qm.adoc
@@ -285,7 +285,7 @@ Even when using a fixed memory size, the ballooning device gets added to the
 VM, because it delivers useful information such as how much memory the guest
 really uses.
 In general, you should leave *ballooning* enabled, but if you want to disable
-it (e.g. for debugging porpuses), simply uncheck
+it (e.g. for debugging purposes), simply uncheck
 *Ballooning* or set
 
  balloon: 0
@@ -421,7 +421,7 @@ If a device is present in a VM configuration when the VM starts up,
 but the device is not present in the host, the VM can boot without problems.
 As soon as the device/port ist available in the host, it gets passed through.
 
-WARNING: Using this kind of USB passthrough, means that you cannot move
+WARNING: Using this kind of USB passthrough means that you cannot move
 a VM online to another host, since the hardware is only available
 on the host the VM is currently residing.
 
@@ -512,10 +512,48 @@ If you have a cluster, you can migrate your VM to another host with
 
  qm migrate <vmid> <target>
 
+There are generally two mechanisms for this
+
+* Online Migration (aka Live Migration)
+* Offline Migration
+
+Online Migration
+~~~~~~~~~~~~~~~~
+
 When your VM is running and it has no local resources defined (such as disks
 on local storage, passed through devices, etc.) you can initiate a live
 migration with the -online flag.
 
+How it works
+^^^^^^^^^^^^
+
+This starts a Qemu Process on the target host with the 'incoming' flag, which
+means that the process starts and waits for the memory data and device states
+from the source Virtual Machine (since all other resources, e.g. disks,
+are shared, the memory content and device state are the only things left
+to transmit).
+
+Once this connection is established, the source begins to send the memory
+content asynchronously to the target. If the memory on the source changes,
+those sections are marked dirty and there will be another pass of sending data.
+This happens until the amount of data to send is so small that it can
+pause the VM on the source, send the remaining data to the target and start
+the VM on the target in under a second.
+
+Requirements
+^^^^^^^^^^^^
+
+For Live Migration to work, there are some things required:
+
+* The VM has no local resources (e.g. passed through devices, local disks, etc.)
+* The hosts are in the same {pve} cluster.
+* The hosts have a working (and reliable) network connection.
+* The target host must have the same or higher versions of the
+  {pve} packages. (It *might* work the other way, but this is never guaranteed)
+
+Offline Migration
+~~~~~~~~~~~~~~~~~
+
 If you have local resources, you can still offline migrate your VMs,
 as long as all disk are on storages, which are defined on both hosts.
 Then the migration will copy the disk over the network to the target host.