Should I protect an Asset using VM, File Agent, or Image Agent backups?


With 10.3 and higher releases, customers have more choices for types of backups methods than prior. This KB will attempt to explain the supported best practices for these varying backup types


With Unitrends Release 10.3 and higher, customers have more choices for types of backups methods than prior.  Each of these methods have different benefits, restrictions, and options depending on several factors clarified in the Unitrends Administrators Guide.  In this KB, we'll attempt to summarize that information into a single source to help better convey the best use cases for each protection model.  
This includes:

  • Performing VM-level backups (also called Host Based backups, or HOS) 
  • Performing Traditional Agent File Backups using in-OS deployed agents (Also referred to as GOS backups), which may also include separate Database level backups
  • Performing Image based backups using in-guest deployed agents (also referred to as block backups)


Simple Best Practices:  As a general rule, unless otherwise eliminated by supported configurations or documented restrictions, the following are loose best practices for determining which type of backup of a particular system to use.  

  • Virtual Machine Backups (HoS) are best where the intended recovery target is back to a hypervisor node of the same platform
  • Image Agent Backups (including those taken using the agent inside a VM) are typically the best in all other scenarios, especially where recovery may involve a Unitrends Physical appliance with Instant Recovery. 
  • File Agent backups (GoS) are best for scenarios for individual systems not supported by the above backup types, or for special scenarios to add backup or recovery flexibility.  If the intent is to support instant recovery of high performance systems, replicas using file backup or VMWare backup may be required.  
  • Application Backups are required for servers hosting Oracle, SharePoint, Exchange DAGs, many SQL AG configurations, and all traditional shared storage cluster systems. 

Common Scenarios that override the above best practices:

  • Backups over a WAN:  WAN backups are not supported.  The deployment of a Unitrends appliance or Endpoint backup solution is required in all cases where a backup must traverse a firewall or gateway.  
  • SQL AG Nodes:  Image backups are recommended for SQL AGs where AG node uses only local storage (no iSCSI, FC, or CSV use by the node).  File Agent + SQL App backups are required for all other AG and SQL Cluster scenarios. 
  • Active Directory Servers: Unitrends recommends using File Agent backups for AD servers where more than 1 AD server is deployed in a domain or forest.  Unitrends recommends using image backups of a DC in environments that have exactly one DC.  AD Admins should also configure and be familiar with Windows wbadmin system state backups that are necessary for some DR scenarios including when it is necessary to roll back AD without first restoring servers.  
  • Microsoft Dynamic Disks: (also applies to any kind of software based RAID system).  File Agent backup is required to access restored disk data granularly.  VM backup is capable only of complete system restore and is supported but not recommended.  Image backups are not compatible.  Other limitations apply.  
  • Windows Native Deduplication:  File Agent backup is recommended where a machine uses native Windows dedupe.  Image and VM backups are supported but may complicate recovery steps of granular files/folders.  


Customers are recommended to perform only one type of backup per client system, and should not perform a combination of Image, File, or VM backups of the same data.  The exceptions to this rule apply only to handling passthru disk protection for VMWare or XenServer platforms using Deep Virtualization.

Before committing to a backup type for a given system, please understand your intended recovery target or targets.  Often when multiple options are supported to protect a particular system, the choice of which is best will be influenced most by where or how you intend to recover that system in the face of a disaster or outage. 

When initially deploying a Unitrends Appliance, or as a post deployment environmental review and best practice alignment, Unitrends offers customers assistance in reviewing best practices for the system included in SureCare professional onboarding services, and with SureCare Complete offers more in depth discussion and training covering overall environment RPO and RTO goals.  You can inquire about this service with your sales representative or reseller.  

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