new faq: How long will my Proxmox VE version be supported?

[pve-docs.git] / pvecm.adoc

diff --git a/pvecm.adoc b/pvecm.adoc
index 1a3a7e8f51b23890e3fadf0b8f0777faa596b34e..6f8b3826c63dd38a9a38593258552a4c6cd0d699 100644 (file)
--- a/pvecm.adoc
+++ b/pvecm.adoc
@@ -59,7 +59,7 @@ Requirements
 * All nodes must be in the same network as corosync uses IP Multicast
  to communicate between nodes (also see
  http://www.corosync.org[Corosync Cluster Engine]). Corosync uses UDP
 * All nodes must be in the same network as corosync uses IP Multicast
  to communicate between nodes (also see
  http://www.corosync.org[Corosync Cluster Engine]). Corosync uses UDP

- ports 5404and 5405 for cluster communication.
+ ports 5404 and 5405 for cluster communication.

 +
 NOTE: Some switches do not support IP multicast by default and must be
 manually enabled first.
 +
 NOTE: Some switches do not support IP multicast by default and must be
 manually enabled first.


@@ -89,7 +89,6 @@ hostname and IP is not possible after cluster creation.
 Currently the cluster creation has to be done on the console, so you
 need to login via 'ssh'.
 
 Currently the cluster creation has to be done on the console, so you
 need to login via 'ssh'.
 

-

 Create the Cluster
 ------------------
 
 Create the Cluster
 ------------------
 


@@ -98,6 +97,10 @@ your cluster. This name cannot be changed later.
 
  hp1# pvecm create YOUR-CLUSTER-NAME
 
 
  hp1# pvecm create YOUR-CLUSTER-NAME
 

+CAUTION: The cluster name is used to compute the default multicast
+address. Please use unique cluster names if you run more than one
+cluster inside your network.
+

 To check the state of your cluster use:
 
  hp1# pvecm status
 To check the state of your cluster use:
 
  hp1# pvecm status


@@ -278,6 +281,50 @@ cluster again, you have to
 * then join it, as explained in the previous section.
 
 
 * then join it, as explained in the previous section.
 
 

+Quorum
+------
+
+{pve} use a quorum-based technique to provide a consistent state among
+all cluster nodes.
+
+[quote, from Wikipedia, Quorum (distributed computing)]
+____
+A quorum is the minimum number of votes that a distributed transaction
+has to obtain in order to be allowed to perform an operation in a
+distributed system.
+____
+
+In case of network partitioning, state changes requires that a
+majority of nodes are online. The cluster switches to read-only mode
+if it loose quorum.
+
+NOTE: {pve} assigns a single vote to each node by default.
+
+
+Cluster Cold Start
+------------------
+
+It is obvious that a cluster is not quorate when all nodes are
+offline. This is a common case after a power failure.
+
+NOTE: It is always a good idea to use an uninterruptible power supply
+('UPS', also called 'battery backup') to avoid this state. Especially if
+you want HA.
+
+On node startup, service 'pve-manager' waits up to 60 seconds to reach
+quorum, and then starts all guests. If it fails to get quorum, that
+service simply aborts, and you need to start your guest manually once
+you have quorum.
+
+If you start all nodes at the same time (for example when power comes
+back), it is likely that you reach quorum within above timeout. But
+startup can fail if some nodes starts much faster than others, so you
+need to start your guest manually after reaching quorum. You can do
+that on the GUI, or on the command line with:
+
+ systemctl start pve-manager
+
+

 ifdef::manvolnum[]
 include::pve-copyright.adoc[]
 endif::manvolnum[]
 ifdef::manvolnum[]
 include::pve-copyright.adoc[]
 endif::manvolnum[]