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, leveraging 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, leveraging transportable shadow copies using hardware VSS provider provided by the SAN storage vendor or SMB3 functionality.
Backup mode availability is heavily depending on the underlying virtualization infrastructure, leaving Off-Host backup mode available only to protect virtual machines hosted on SAN storage volumes 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 is highly recommended (cluster environment).
Performance wise, since both backup modes are using the exact same Veeam transport services, 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.
|On-Host||Simplifies management |
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
|Requires additional resources from the hypervisors (CPU, Network IO and RAM) during the backup window, for IO processing and optimization|
|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
Might depend on 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. It should be kept in mind that the backup load, instead of being carried by a limited number of dedicated proxies, will be spread over all Hyper-V hosts. When needing 16 proxy task slots to meet the backup window, in a cluster of 8 hosts each hosting the same amount of proteced VMs will result in 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 section of the User Guide for further information.