Storage Replication: Difference between revisions

Latest revision as of 14:11, 23 November 2023

The pvesr command-line tool manages the Proxmox VE storage replication framework. Storage replication brings redundancy for guests using local storage and reduces migration time.

It replicates guest volumes to another node so that all data is available without using shared storage. Replication uses snapshots to minimize traffic sent over the network. Therefore, new data is sent only incrementally after the initial full sync. In the case of a node failure, your guest data is still available on the replicated node.

The replication is done automatically in configurable intervals. The minimum replication interval is one minute, and the maximal interval once a week. The format used to specify those intervals is a subset of systemd calendar events, see Schedule Format section:

It is possible to replicate a guest to multiple target nodes, but not twice to the same target node.

Each replications bandwidth can be limited, to avoid overloading a storage or server.

Only changes since the last replication (so-called deltas) need to be transferred if the guest is migrated to a node to which it already is replicated. This reduces the time needed significantly. The replication direction automatically switches if you migrate a guest to the replication target node.

For example: VM100 is currently on nodeA and gets replicated to nodeB. You migrate it to nodeB, so now it gets automatically replicated back from nodeB to nodeA.

If you migrate to a node where the guest is not replicated, the whole disk data must send over. After the migration, the replication job continues to replicate this guest to the configured nodes.

High-Availability is allowed in combination with storage replication, but there may be some data loss between the last synced time and the time a node failed.

Supported Storage Types

Table 1. Storage Types
Description	Plugin type	Snapshots	Stable
ZFS (local)	zfspool	yes	yes

Schedule Format

Replication uses calendar events for configuring the schedule.

Error Handling

If a replication job encounters problems, it is placed in an error state. In this state, the configured replication intervals get suspended temporarily. The failed replication is repeatedly tried again in a 30 minute interval. Once this succeeds, the original schedule gets activated again.

Possible issues

Some of the most common issues are in the following list. Depending on your setup there may be another cause.

Network is not working.
No free space left on the replication target storage.
Storage with same storage ID available on the target node

You can always use the replication log to find out what is causing the problem.

Migrating a guest in case of Error

In the case of a grave error, a virtual guest may get stuck on a failed node. You then need to move it manually to a working node again.

Example

Let’s assume that you have two guests (VM 100 and CT 200) running on node A and replicate to node B. Node A failed and can not get back online. Now you have to migrate the guest to Node B manually.

connect to node B over ssh or open its shell via the web UI
check if that the cluster is quorate
```
# pvecm status
```
If you have no quorum, we strongly advise to fix this first and make the node operable again. Only if this is not possible at the moment, you may use the following command to enforce quorum on the current node:
```
# pvecm expected 1
```

Avoid changes which affect the cluster if expected votes are set (for example adding/removing nodes, storages, virtual guests) at all costs. Only use it to get vital guests up and running again or to resolve the quorum issue itself.

move both guest configuration files form the origin node A to node B:

# mv /etc/pve/nodes/A/qemu-server/100.conf /etc/pve/nodes/B/qemu-server/100.conf
# mv /etc/pve/nodes/A/lxc/200.conf /etc/pve/nodes/B/lxc/200.conf

Now you can start the guests again:
```
# qm start 100
# pct start 200
```

Remember to replace the VMIDs and node names with your respective values.

Managing Jobs

screenshot/gui-qemu-add-replication-job.png

You can use the web GUI to create, modify, and remove replication jobs easily. Additionally, the command-line interface (CLI) tool pvesr can be used to do this.

You can find the replication panel on all levels (datacenter, node, virtual guest) in the web GUI. They differ in which jobs get shown: all, node- or guest-specific jobs.

When adding a new job, you need to specify the guest if not already selected as well as the target node. The replication schedule can be set if the default of all 15 minutes is not desired. You may impose a rate-limit on a replication job. The rate limit can help to keep the load on the storage acceptable.

A replication job is identified by a cluster-wide unique ID. This ID is composed of the VMID in addition to a job number. This ID must only be specified manually if the CLI tool is used.

Command-line Interface Examples

Create a replication job which runs every 5 minutes with a limited bandwidth of 10 Mbps (megabytes per second) for the guest with ID 100.

# pvesr create-local-job 100-0 pve1 --schedule "*/5" --rate 10

Disable an active job with ID 100-0.

# pvesr disable 100-0

Enable a deactivated job with ID 100-0.

# pvesr enable 100-0

Change the schedule interval of the job with ID 100-0 to once per hour.

# pvesr update 100-0 --schedule '*/00'

@@ Line 4: / Line 4: @@
 [[Category:Reference Documentation]]
 <pvehide>
-The pvesr command line tool manages the Proxmox VE storage replication
+The pvesr command-line tool manages the Proxmox VE storage replication
 framework. Storage replication brings redundancy for guests using
 local storage and reduces migration time.
@@ Line 10: / Line 10: @@
 without using shared storage. Replication uses snapshots to minimize traffic
 sent over the network. Therefore, new data is sent only incrementally after
-an initial full sync. In the case of a node failure, your guest data is
+the initial full sync. In the case of a node failure, your guest data is
 still available on the replicated node.
-The replication will be done automatically in configurable intervals.
+The replication is done automatically in configurable intervals.
-The minimum replication interval is one minute and the maximal interval is
+The minimum replication interval is one minute, and the maximal interval
 once a week. The format used to specify those intervals is a subset of
 systemd calendar events, see
 Schedule Format section:
-Every guest can be replicated to multiple target nodes, but a guest cannot
+It is possible to replicate a guest to multiple target nodes,
-get replicated twice to the same target node.
+but not twice to the same target node.
 Each replications bandwidth can be limited, to avoid overloading a storage
 or server.
-Virtual guest with active replication cannot currently use online migration.
+Only changes since the last replication (so-called deltas) need to be
-Offline migration is supported in general. If you migrate to a node where
+transferred if the guest is migrated to a node to which it already is
-the guests data is already replicated only the changes since the last
+replicated. This reduces the time needed significantly. The replication
-synchronisation (so called delta) must be sent, this reduces the required
+direction automatically switches if you migrate a guest to the replication
-time significantly. In this case the replication direction will also switch
+target node.
-nodes automatically after the migration finished.
 For example: VM100 is currently on nodeA and gets replicated to nodeB.
 You migrate it to nodeB, so now it gets automatically replicated back from
 nodeB to nodeA.
 If you migrate to a node where the guest is not replicated, the whole disk
-data must send over. After the migration the replication job continues to
+data must send over. After the migration, the replication job continues to
 replicate this guest to the configured nodes.
-High-Availability is allowed in combination with storage replication, but it
+High-Availability is allowed in combination with storage replication, but there
-has the following implications:
+may be some data loss between the last synced time and the time a node failed.
-redistributing services after a more preferred node comes online will lead
-  to errors.
-recovery works, but there may be some data loss between the last synced
-  time and the time a node failed.
 Supported Storage Types
 Table 1. Storage Types
 Description
-PVE type
+Plugin type
 Snapshots
 Stable
@@ Line 50: / Line 45: @@
 yes
 Schedule Format
-Proxmox VE has a very flexible replication scheduler. It is based on the systemd
+Replication uses calendar events for
-time calendar event format.[see man 7 sytemd.time for more information]
+configuring the schedule.
-Calendar events may be used to refer to one or more points in time in a
-single expression.
-Such a calendar event uses the following format:
-[day(s)] [[start-time(s)][/repetition-time(s)]]
-This allows you to configure a set of days on which the job should run.
-You can also set one or more start times, it tells the replication scheduler
-the moments in time when a job should start.
-With this information we could create a job which runs every workday at 10
-PM: 'mon,tue,wed,thu,fri 22' which could be abbreviated to: 'mon..fri
-', most reasonable schedules can be written quite intuitive this way.
-Hours are set in 24h format.
-To allow easier and shorter configuration one or more repetition times can
-be set. They indicate that on the start-time(s) itself and the start-time(s)
-plus all multiples of the repetition value replications will be done.  If
-you want to start replication at 8 AM and repeat it every 15 minutes you
-would use: '8:00/15'
-Here you see also that if no hour separation (:) is used the value gets
-interpreted as minute. If such a separation is used the value on the left
-denotes the hour(s) and the value on the right denotes the minute(s).
-Further, you can use * to match all possible values.
-To get additional ideas look at
-more Examples below.
-Detailed Specification
-days
-Days are specified with an abbreviated English version: sun, mon,
-tue, wed, thu, fri and sat. You may use multiple days as a comma-separated
-list. A range of days can also be set by specifying the start and end day
-separated by &#8220;..&#8221;, for example mon..fri. Those formats can be also
-mixed. If omitted '*' is assumed.
-time-format
-A time format consists of hours and minutes interval lists.
-Hours and minutes are separated by ':'. Both, hour and minute, can be list
-and ranges of values, using the same format as days.
-First come hours then minutes, hours can be omitted if not needed, in this
-case '*' is assumed for the value of hours.
-The valid range for values is 0-23 for hours and 0-59 for minutes.
-Examples:
-Table 2. Schedule Examples
-Schedule String
-Alternative
-Meaning
-mon,tue,wed,thu,fri
-mon..fri
-All working days at 0:00
-sat,sun
-sat..sun
-Only on weekend at 0:00
-mon,wed,fri
-&#8212;&#8201;
-Only on Monday, Wednesday and Friday at 0:00
-:05
-:05
-All weekdays at 12:05 PM
-*/5
-/5
-Every day all five minutes
-mon..wed 30/10
-mon,tue,wed 30/10
-Monday, Tuesday, Wednesday 30, 40 and 50 minutes after every full hour
-mon..fri 8..17,22:0/15
-&#8212;&#8201;
-All working days every 15 minutes between 8 AM and 5 PM plus at 10 PM
-fri 12..13:5/20
-fri 12,13:5/20
-Friday at 12:05, 12:25, 12:45, 13:05, 13:25 and 13:45
-..22:5/2
-:5/2
-Every day starting at 12:05 until 22:05 all 2 hours
-*
-*/1
-Every minute (minimum interval)
 Error Handling
-If a replication job encounters problems it will be placed in error state.
+If a replication job encounters problems, it is placed in an error state.
-In this state the configured replication intervals get suspended
+In this state, the configured replication intervals get suspended
-temporarily. Then we retry the failed replication in a 30 minute interval,
+temporarily. The failed replication is repeatedly tried again in a
-once this succeeds the original schedule gets activated again.
+minute interval.
+Once this succeeds, the original schedule gets activated again.
 Possible issues
-This represents only the most common issues possible, depending on your
+Some of the most common issues are in the following list. Depending on your
-setup there may be also another cause.
+setup there may be another cause.
 Network is not working.
 No free space left on the replication target storage.
-Storage with same storage ID available on target node
+Storage with same storage ID available on the target node
-You can always use the replication log to get hints about a problems
+You can always use the replication log to find out what is causing the problem.
-cause.
 Migrating a guest in case of Error
-In the case of a grave error a virtual guest may get stuck on a failed
+In the case of a grave error, a virtual guest may get stuck on a failed
 node. You then need to move it manually to a working node again.
 Example
-Lets assume that you have two guests (VM 100 and CT 200) running on node A
+Let&#8217;s assume that you have two guests (VM 100 and CT 200) running on node A
 and replicate to node B.
 Node A failed and can not get back online. Now you have to migrate the guest
 to Node B manually.
-connect to node B over ssh or open its shell via the WebUI
+connect to node B over ssh or open its shell via the web UI
 check if that the cluster is quorate
 # pvecm status
-If you have no quorum we strongly advise to fix this first and make the
+If you have no quorum, we strongly advise to fix this first and make the
-   node operable again. Only if this is not possible at the moment you may
+   node operable again. Only if this is not possible at the moment, you may
    use the following command to enforce quorum on the current node:
 # pvecm expected 1
-If expected votes are set avoid changes which affect the cluster
+Avoid changes which affect the cluster if expected votes are set
-(for example adding/removing nodes, storages, virtual guests)  at all costs.
+(for example adding/removing nodes, storages, virtual guests) at all costs.
-Only use it to get vital guests up and running again or to resolve to quorum
+Only use it to get vital guests up and running again or to resolve the quorum
 issue itself.
 move both guest configuration files form the origin node A to node B:
-# mv /etc/pve/node/A/qemu-server/100.conf /etc/pve/node/B/qemu-server/100.conf
+# mv /etc/pve/nodes/A/qemu-server/100.conf /etc/pve/nodes/B/qemu-server/100.conf
-# mv /etc/pve/node/A/lxc/200.conf /etc/pve/node/B/lxc/200.conf
+# mv /etc/pve/nodes/A/lxc/200.conf /etc/pve/nodes/B/lxc/200.conf
 Now you can start the guests again:
 # qm start 100
@@ Line 163: / Line 87: @@
 Remember to replace the VMIDs and node names with your respective values.
 Managing Jobs
-You can use the web GUI to create, modify and remove replication jobs
+You can use the web GUI to create, modify, and remove replication jobs
-easily. Additionally the command line interface (CLI) tool pvesr can be
+easily. Additionally, the command-line interface (CLI) tool pvesr can be
 used to do this.
 You can find the replication panel on all levels (datacenter, node, virtual
-guest) in the web GUI. They differ in what jobs get shown: all, only node
+guest) in the web GUI. They differ in which jobs get shown:
-specific or only guest specific jobs.
+all, node- or guest-specific jobs.
-Once adding a new job you need to specify the virtual guest (if not already
+When adding a new job, you need to specify the guest if not already selected
-selected) and the target node. The replication
+as well as the target node. The replication
 schedule can be set if the default of all
-minutes is not desired. You may also impose rate limiting on a
+minutes is not desired. You may impose a rate-limit on a replication
-replication job, this can help to keep the storage load acceptable.
+job. The rate limit can help to keep the load on the storage acceptable.
-A replication job is identified by an cluster-wide unique ID. This ID is
+A replication job is identified by a cluster-wide unique ID. This ID is
-composed of the VMID in addition to an job number.
+composed of the VMID in addition to a job number.
 This ID must only be specified manually if the CLI tool is used.
-Command Line Interface Examples
+Command-line Interface Examples
-Create a replication job which will run all 5 min with limited bandwidth of
+Create a replication job which runs every 5 minutes with a limited bandwidth
-mbps (megabytes per second) for the guest with guest ID 100.
+of 10 Mbps (megabytes per second) for the guest with ID 100.
 # pvesr create-local-job 100-0 pve1 --schedule "*/5" --rate 10
-Disable an active job with ID 100-0
+Disable an active job with ID 100-0.
 # pvesr disable 100-0
-Enable a deactivated job with ID 100-0
+Enable a deactivated job with ID 100-0.
 # pvesr enable 100-0
-Change the schedule interval of the job with ID 100-0 to once a hour
+Change the schedule interval of the job with ID 100-0 to once per hour.
 # pvesr update 100-0 --schedule '*/00'
 </pvehide>
 <!--PVE_IMPORT_END_MARKER-->