There are various considerations of using either image or guest backup to protect virtual machine data.
General use case guidelines
For virtual machines hosted in a vCenter, image backup enables you to protect multiple virtual machines with the least amount of effort.
On Windows Vista/2008 and later virtual machines, image backups are fully application-consistent and sufficient for most use cases involving Microsoft Exchange, Microsoft Office SharePoint, and Microsoft SQL Server. However, because image backup is limited to functionality offered by the VMware vStorage API for Data Protection (VADP), some deployments might require more advanced functionality than that offered by VADP. In these situations, the additional functionality that is provided by guest backup might offer a better solution.
The following deployments are known to benefit from using guest backup instead of image backup:
Exchange Database Availability Groups (DAGs)
SharePoint Server Farms
SharePoint deployments requiring log truncation
Guest backup is the only way to protect virtual machines that are not hosted in a vCenter (for example, desktops and laptops).
Ease of implementation
Image backup:
Can leverage vCenter to discover virtual machines, and add them to the Avamar server in batches.
Requires a moderate amount of initial setup and configuration.
Guest backup:
Supports any virtual machine running an operating system for which Avamar client software is available.
Supports applications such as DB2, Exchange, Oracle, and SQL Server databases.
Easily fits into most existing backup schemes; day-to-day backup procedures do not change.
Avamar client software must be individually installed, and managed inside each virtual machine.
Efficiency
Image backup:
Offers moderate deduplication efficiency.
Does not consume guest virtual machine CPU, RAM, and disk resources during backups.
Does consume ESX Server CPU, RAM, and disk resources during backups.
Guest backup:
Offers the highest level of data deduplication efficiency.
Does consume small amounts of guest virtual machine CPU, RAM, and disk resources during backups.
Does not consume ESX Server CPU, RAM, and disk resources during backups.
Backup and restore
Image backup:
Image backups are supported for all machines currently supported by VMware.
Backups can comprise an entire virtual machine image (all drives) or selected drives (.vmdk files).
Individual folder and file restores supported for both Windows and Linux virtual machines.
Backups are not optimized (temp files, swap files, and so forth, are included).
Unused file system space is backed up.
Virtual machines need not have a network connection to Avamar server.
Virtual machines need not be running for backups to occur.
Guest backup:
Backups are highly optimized (temp files, swap files, and so forth, are not included).
Backups are highly customizable (supports full range of include and exclude features).
Database backups support transaction log truncation, and other advanced features.
Unused file system space is not backed up.
Individual folder and file restores are supported for all supported virtual machines (not just Linux and Windows)
Backup and restore jobs can execute pre- and post-processing scripts.
Virtual machines must have a network connection to Avamar server.
Virtual machines must be running for backups to occur.
Required VMware knowledge
Image backup requires moderate VMware knowledge. Integrators should have working knowledge of the vCenter topology in use at that customer site (that is, which ESX Servers host each datastore, and which datastores store each virtual machine’s data), and the ability to log in to vCenter with administrator privileges.
Guest backup and restore requires no advanced scripting or VMware knowledge.
Using both image and guest backup
A virtual machine can be protected by both guest backup and image backup. For example, a daily guest backup might be used to protect selective files, and a less frequent or on-demand full image backup might be used to protect the full machine. This scheme accommodates scenarios with limited backup windows.
To support using both image and guest backup to protect the same virtual machine, you must configure the Avamar MCS to allow duplicate client names.
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