NAME
----
-pvecm - Proxmox VE Cluster Manager
+pvecm - {pve} Cluster Manager
SYNOPSYS
--------
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-The {PVE} cluster manager 'pvecm' is a tool to create a group of
-physical servers. Such group is called a *cluster*. We use the
+The {PVE} cluster manager `pvecm` is a tool to create a group of
+physical servers. Such a group is called a *cluster*. We use the
http://www.corosync.org[Corosync Cluster Engine] for reliable group
-communication, and such cluster can consists of up to 32 physical nodes
+communication, and such clusters can consist of up to 32 physical nodes
(probably more, dependent on network latency).
-'pvecm' can be used to create a new cluster, join nodes to a cluster,
+`pvecm` can be used to create a new cluster, join nodes to a cluster,
leave the cluster, get status information and do various other cluster
-related tasks. The Proxmox Cluster file system (pmxcfs) is used to
-transparently distribute the cluster configuration to all cluster
+related tasks. The **P**rox**m**o**x** **C**luster **F**ile **S**ystem (``pmxcfs'')
+is used to transparently distribute the cluster configuration to all cluster
nodes.
Grouping nodes into a cluster has the following advantages:
* Centralized, web based management
-* Multi-master clusters: Each node can do all management task
+* Multi-master clusters: each node can do all management task
-* Proxmox Cluster file system (pmxcfs): Database-driven file system
- for storing configuration files, replicated in real-time on all
- nodes using corosync.
+* `pmxcfs`: database-driven file system for storing configuration files,
+ replicated in real-time on all nodes using `corosync`.
-* Easy migration of Virtual Machines and Containers between physical
+* Easy migration of virtual machines and containers between physical
hosts
* Fast deployment
Requirements
------------
-* All nodes must be in the same network as corosync uses IP Multicast
+* 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 5404 and 5405 for cluster communication.
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'.
+need to login via `ssh`.
Create the Cluster
------------------
-Login via 'ssh' to the first Proxmox VE node. Use a unique name for
-your cluster. This name cannot be changed later.
+Login via `ssh` to the first {pve} node. Use a unique name for your cluster.
+This name cannot be changed later.
hp1# pvecm create YOUR-CLUSTER-NAME
Adding Nodes to the Cluster
---------------------------
-Login via 'ssh' to the node you want to add.
+Login via `ssh` to the node you want to add.
hp2# pvecm add IP-ADDRESS-CLUSTER
For `IP-ADDRESS-CLUSTER` use the IP from an existing cluster node.
-CAUTION: A new node cannot hold any VMยดs, because you would get
+CAUTION: A new node cannot hold any VMs, because you would get
conflicts about identical VM IDs. Also, all existing configuration in
-'/etc/pve' is overwritten when you join a new node to the cluster. To
-workaround, use vzdump to backup and restore to a different VMID after
+`/etc/pve` is overwritten when you join a new node to the cluster. To
+workaround, use `vzdump` to backup and restore to a different VMID after
adding the node to the cluster.
To check the state of cluster:
# pvecm nodes
-.List Nodes in a Cluster
+.List nodes in a cluster
----
hp2# pvecm nodes
Move all virtual machines from the node. Make sure you have no local
data or backups you want to keep, or save them accordingly.
-Log in to one remaining node via ssh. Issue a 'pvecm nodes' command to
+Log in to one remaining node via ssh. Issue a `pvecm nodes` command to
identify the node ID:
----
----
Log in to one remaining node via ssh. Issue the delete command (here
-deleting node hp4):
+deleting node `hp4`):
hp1# pvecm delnode hp4
If the operation succeeds no output is returned, just check the node
-list again with 'pvecm nodes' or 'pvecm status'. You should see
+list again with `pvecm nodes` or `pvecm status`. You should see
something like:
----
If, for whatever reason, you want that this server joins the same
cluster again, you have to
-* reinstall pve on it from scratch
+* reinstall {pve} on it from scratch
* 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 loses 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` is started and waits for
+quorum. Once quorate, it starts all guests which have the `onboot`
+flag set.
+
+When you turn on nodes, or when power comes back after power failure,
+it is likely that some nodes boots faster than others. Please keep in
+mind that guest startup is delayed until you reach quorum.
+
+
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projects / pve-docs.git / blobdiff