Veeam Backup and Replication provides two different backup modes to process Hyper-V backups, both relying on the Microsoft VSS framework.
- On-Host backup mode, for which backup data processing is on the Hyper-V node hosting the VM. It leverages non transportable shadow copies by using software VSS provider.
- Off-Host backup mode, for which backup data processing is offloaded to another non-clustered participating Hyper-V node. It leverages transportable shadow copies using hardware VSS provider provided by the SAN storage vendor or SMB3 functionality.
Backup mode availability depends on the underlying virtualization infrastructure. Off-Host backup mode works for virtual machines hosted on SAN storage or SMB3 compatible storage. It is important that the VSS framework provided by the storage vendor is tested and certified to work with Microsoft Hyper-V clusters. Intensive checks of vendor VSS provider during POC are highly recommended (cluster environment).
Performance wise, since both backup modes are using the same Veeam transport service, the only differentiating factors will be the additional time requested to manage transportable snapshots (in favor of On-Host mode) and the balance between compute and backup resources consumption during backup windows (in favor of Off-Host mode).
When using Windows Server 2016 or later, On-Host proxy mode is very fast and requires less components, thus reduces complexity. However, the Veeam data mover agent will consume host compute resources for deduplication and compression, so this needs to be considered when planning the Veeam Job design. Please be aware that you will need up to 2GB of RAM on the Hyper-V Host per running task (one task = backup of one virtual disk). This memory must be available for running backup jobs, otherwise the Hyper-V Host will start paging, which will result in an overall slow system.
Wherever feasible the recommendation is to use on-host proxy mode.
|On-Host||Simplifies management||Requires additional resources from the hypervisors (CPU, Network IO and RAM) during the backup window, for IO processing and optimization|
|Does not require additional hardware, load is spread over all Hyper-V hosts|
|Can be used on any Hyper-V infrastructure|
|Scales with virtualization environment|
|Off-Host||No impact on the compute resources on the hosting Hyper-V Server||Adds additional delay for snapshots transportation||Requires compatible SAN or SMB3 storage|
|Depends on stability of third party VSS provider|
While consuming production resources for backup purposes, the On-Host backup mode disadvantages can be mitigated by the following guidelines.
Spreading load across hypervisors. The backup load will automatically be spread over all Hyper-V hosts.
Example: Let’s assume sizing calculation results in 16 CPU cores being required to achieve your backup window. In a cluster of 8 hosts, each hosting the same amount of protected VMs, this makes a task limit configuration of 2 per host, thus limiting the impact per host.
Leveraging storage latency control. This feature allows to protect the volumes (globally for Enterprise edition, and individually for Enterprise Plus edition) from high latency, by monitoring and adjusting backup load accordingly. Please refer to [Specifying I/O Settings][veeam helpcenter - specifying i/o settings] section of the User Guide for further information.