The Virtual Server Agent (VSA) proxy on a XenServer can perform backups for all virtual machines (VMs) running on shared storage. The best practice approach is to deploy at least one proxy in each Xen pool. For XenServers with high backup requirements, multiple proxies can be deployed.
By default, a backup takes a quiesced snapshot for each VM, using the Windows Volume Shadow Copy Service (VSS) to generate an application-consistent point-in-time snapshot as a source for the backup. If the backup is unable to take a quiesced snapshot, the backup takes a disk-only snapshot instead. For more information, see About Snapshots in XenCenter documentation.
Note
With XenServer 6.x, a VSA proxy for Xen can have a maximum of 16 disks attached, including any disks that belong to the proxy as well as VM disks that are included with a backup or restore operation. If the disk limit is exceeded during a backup operation, the operation fails.
Virtual machine backup jobs are allocated to VSA proxies according to the following priorities:
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Each VSA proxy manages backups for virtual machines hosted on the same XenServer.
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If a proxy on the same host is not available, another VSA proxy that has access to the VM storage repository is used.
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When multiple VSA proxies are available for a host, the round-robin method is used to choose the least loaded proxy.
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If none of the other criteria can be used to allocate jobs for a VM, jobs are allocated by default to the coordinator node (the first VSA proxy listed for the virtualization client). If the coordinator node cannot access the storage repositories for the VM disks, the job fails.
When a virtual machine is discovered during backup, a client for the VM is created in the CommCell Console if one does not already exist. If a virtual machine with spaces or special characters in its name is discovered during backup, the spaces or special characters are replaced with underscores ('_') when creating the VM client name that is displayed in the CommCell Console. The VM name with spaces or special characters is still displayed on the Virtual Machine Status tab for the backup job, in the backup job summary, and in reports that include the VM name. The following special characters are replaced:
[ \ \ | ` ~ ! @ # $ % ^ & * + = < > ? , { } ( ) : ; ' \ " \ \ s / ]What Gets Backed Up
The VSA backs up the following data:
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Virtual machines (powered on or powered off)
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Associated virtual machine disks
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When a virtual machine disk for a Xen virtual machine is backed up, the entire disk is read for allocated blocks, for both full and incremental backups.
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Custom templates
What Does Not Get Backed Up
The VSA does not back up the following data:
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Proxy virtual machines on which the Virtual Server Agent is installed
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Citrix Hypervisor templates
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Physical disks attached to a guest VM
Note
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If some parts of a virtual machine backup job are not completed successfully, the job status is "Completed w/ one or more errors". To check the status of specific VMs, you can view the Job Details dialog box and then select the Virtual Machine Status tab.
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If the status for a specific virtual machine is "Partial Success", some information for the VM was successfully backed up, but other information was not. Failed items for a VM contribute to the Failed Objects count in the Backup Job Summary Report.
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A VM is included in a backup of failed VMs only if the VM is marked as "Failed" in the Virtual Machine Status tab. VMs that complete with partial success are not included as failed VMs.
Controlling Metadata Collection and Granular Recovery
By default, file and folder metadata is collected during backups. Metadata collection is required for recovery of guest files and folders from virtual machines.
If you do not need to recover file and folder information for some virtual machines, you can configure backups to disable the granular recovery option.
Backup Types
You can perform the following types of backups, either immediately or on a schedule:
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Back up the entire virtual machine. This is the most comprehensive backup.
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Back up virtual machine data that has changed since the most recent backup.
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Back up virtual machine data that has changed since the most recent full backup.
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Consolidate virtual machine data from the most recent full backup with subsequent incremental and differential backups.