Hyper-V Backup Modes
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 and Performance Considerations
Backup mode availability is dependent on the underlying virtualization infrastructure. Off-Host backup mode is compatible with virtual machines hosted on SAN storage or SMB3 compatible storage. It is crucial that the VSS framework provided by the storage vendor is tested and certified to work with Microsoft Hyper-V clusters. Intensive checks of the vendor’s VSS provider during the proof of concept (POC) phase are highly recommended.
From a performance perspective, since both backup modes utilize the same Veeam transport service, the primary differentiating factors are the additional time required to request and manage transportable snapshots (favoring On-Host mode) and the balance between compute and backup resource consumption during backup windows (favoring Off-Host mode).
When using Hyper-V 2016 or later, On-Host proxy mode is very efficient and requires fewer components, thereby reducing complexity. However, the Veeam data mover agent will consume host compute resources for deduplication and compression, which should be considered when planning the Veeam job design. Note that up to 2GB of RAM per running task (one task = backup of one virtual disk) is required on the Hyper-V Host. This memory must be available for running backup jobs; otherwise, the Hyper-V Host will start paging, resulting in an overall slower system.
Wherever feasible, the recommendation is to use On-Host proxy mode.
Backup modes selection matrix
| PRO | CON | ||
|---|---|---|---|
| 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 | |||
Limiting the impact of On-Host backup mode on the production infrastructure
While consuming production resources for backup purposes, the On-Host backup mode disadvantages can be mitigated by the following guidelines.
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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.
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Leveraging storage latency control. This feature allows to protect the volumes from high latency situations by monitoring and adjusting backup load accordingly. Please refer to Specifying I/O Settings section of the User Guide for further information.