vzdump: minimally rework backup notes, mostly formatting

[pve-docs.git] / pvecm.adoc

diff --git a/pvecm.adoc b/pvecm.adoc
index 48c3927cb17ec1791e62106985854141fc64f8bd..2af682825a8b062a1926b80f617d4482431319c7 100644 (file)
--- a/pvecm.adoc
+++ b/pvecm.adoc
@@ -511,11 +511,18 @@ file system (`pmxcfs`).
 [[pvecm_cluster_network_requirements]]
 Network Requirements
 ~~~~~~~~~~~~~~~~~~~~
-This needs a reliable network with latencies under 2 milliseconds (LAN
-performance) to work properly. The network should not be used heavily by other
-members; ideally corosync runs on its own network. Do not use a shared network
-for corosync and storage (except as a potential low-priority fallback in a
-xref:pvecm_redundancy[redundant] configuration).
+
+The {pve} cluster stack requires a reliable network with latencies under 5
+milliseconds (LAN performance) between all nodes to operate stably. While on
+setups with a small node count a network with higher latencies _may_ work, this
+is not guaranteed and gets rather unlikely with more than three nodes and
+latencies above around 10 ms.
+
+The network should not be used heavily by other members, as while corosync does
+not uses much bandwidth it is sensitive to latency jitters; ideally corosync
+runs on its own physically separated network.  Especially do not use a shared
+network for corosync and storage (except as a potential low-priority fallback
+in a xref:pvecm_redundancy[redundant] configuration).
 
 Before setting up a cluster, it is good practice to check if the network is fit
 for that purpose. To ensure that the nodes can connect to each other on the
@@ -974,9 +981,9 @@ the cluster and to have a corosync-qnetd package available. We provide a package
 for Debian based hosts, and other Linux distributions should also have a package
 available through their respective package manager.
 
-NOTE: In contrast to corosync itself, a QDevice connects to the cluster over
-TCP/IP. The daemon may even run outside of the cluster's LAN and can have longer
-latencies than 2 ms.
+NOTE: Unlike corosync itself, a QDevice connects to the cluster over TCP/IP.
+The daemon can also run outside the LAN of the cluster and isn't limited to the
+low latencies requirements of corosync.
 
 Supported Setups
 ~~~~~~~~~~~~~~~~
@@ -1044,6 +1051,8 @@ The SSH key from the cluster will be automatically copied to the QDevice.
 
 NOTE: Make sure that the SSH configuration on your external server allows root
 login via password, if you are asked for a password during this step.
+If you receive an error such as 'Host key verification failed.' at this
+stage, running `pvecm updatecerts` could fix the issue.
 
 After you enter the password and all the steps have successfully completed, you
 will see "Done". You can verify that the QDevice has been set up with: