Sizing a Backup Proxy

Getting the right amount of processing power is essential to achieving the RTO/RPO defined by the business. In this section, we will outline the recommendations to follow for appropriate sizing.

Processing Resources

As described above, you may define the max concurrent tasks value in the backup proxy settings. It is best practices to plan for 1 physical core or 1 vCPU and 2 GB of RAM for each of the tasks. A task processes 1 VM disk at a time and CPU/RAM resources are used for inline data deduplication, compression, encryption and other features that are running on the proxy itself.

In the User Guide it is stated that proxy servers require 2 GB RAM + 500 MB per task. Please consider these values as minimum requirements. Using the above mentioned recommendations allow for growth and additional inline processing features or other special job settings that increase RAM consumption.

If the proxy is used for other roles like Gateway Server for SMB shares, EMC DataDomain DDBoost, HPE StoreOnce Catalyst or if you run the backup repository on the server, remember stacking system requirements for all the different components. Please see related chapters for each components for further details.

Tip: Doubling the proxy server task count will - in general - reduce the backup window by 2x.

Calculating required proxy tasks

Depending on the infrastructure and source storage performance, these numbers may turn out being too conservative. We recommend to performing a POC to examine the specific numbers for the environment.


Our sample infrastructure has the following characteristics:

  • 1,000 VMs

  • 100 TB of consumed storage

  • 8 hours backup window

  • 10% change rate

By inserting these numbers into the equations above, we get the following results.

We use the average throughput to predict how many cores are required to meet the defined SLA.

The equation is modified to account for decreased performance for incremental backups in the following result:

As seen above, incremental backups typically have lower compute requirements, on the proxy servers.

Considering each task consumes up to 2 GB RAM, we get the following result:

36 cores and 72 GB RAM

  • For a physical server, it is recommended to install dual CPUs with 10 cores each.

    2 physical servers are required.

  • For virtual proxy servers, it is recommended to configure multiple proxies

    with maximum 8 vCPUs to avoid co-stop scheduling issues. 5 virtual proxy

    servers are required.

If we instead size only for incremental backups rather than full backups, we can predict alternative full backup window with less compute:

If the business can accept this increased backup window for periodical full backups, it is possible to lower the compute requirement by more than 2x and get the following result:

14 cores and 28 GB RAM

  • For a physical server, it is recommended to install dual CPUs with 10 cores each.

    1 physical server is required.

  • For virtual proxy servers, it is recommended to configure multiple proxies

    with maximum 8 vCPUs to avoid co-stop scheduling issues. 2 virtual proxy

    servers are required.

If you need to achieve a 2x smaller backup window (4 hours), then you may double the resources - 2x the amount of compute power (split across multiple servers).

The same rule applies if the change rate is 2x higher (20% change rate). To process a 2x increase in amount of changed data, it is also required to double the proxy resources.

Note: Performance largely depends on the underlying storage and network infrastructure.

Required processing resources may seem too high if compared with traditional agent-based solutions. However, consider that instead of using all VMs as processing power for all backup operations (including data transport, source deduplication and compression), Veeam Backup & Replication uses its proxy and repository resources to offload the virtual infrastructure. Overall, required CPU and RAM resources utilized by backup and replication jobs are typically below 5% (and in many cases below 3%) of all virtualization resources.

How many VMs per job?

  • For per job backup files: 30 VMs per job

  • For per VM backup files: 300 VMs per job

Consider that some tasks within a job are still sequential processes. For example, a merge process writing the oldest incremental file into the full backup file is started after the last VM finishes backup processing. If you split the VMs into multiple jobs these background processes are parallelized and overall backup window can be lower. Be as well careful with big jobs when you use Storage Snapshots at Backup from Storage Snapshots. Guest processing and Scheduling of jobs that contain multiple snapshots can lead into difficult scheduling situation and jobs spending time waiting for (free) resources. A good size for jobs that write to per VM chain enabled repositories is 50-200 VMs per Job.

Also, remember that the number of concurrently running backup jobs should not exceed 100. Veeam can handle more, but a “sweet spot” for database load, load balancing and overall processing is about 80-100 concurrently running jobs.

How Many Tasks per Proxy?

Typically, in a virtual environment, proxy servers use 4, 6 or 8 vCPUs, while in physical environments you can use a server with a single quad core CPU for small sites, while more powerful systems (dual 10-16 core CPU) are typically deployed at the main datacenter with the Direct SAN Access processing mode.

Note: Parallel processing may also be limited by max concurrent tasks at the repository level.

So, in a virtual-only environment you will have slightly more proxies with a smaller proxy task slot count, while in a physical infrastructure with good storage connection you will have a very high parallel proxy task count per proxy.

The “sweet spot” in a physical environment is about 20 processing tasks on a 2x10 Core CPU proxy with 48GB RAM and two 16 Gbps FC cards for read, plus one or two 10GbE network cards.

Depending on the primary storage system and backup target storage system, any of the following methods can be recommended to reach the best backup performance:

  • Running fewer proxy tasks with a higher throughput per current proxy task

  • Running higher proxy task count with less throughput per task

As performance depends on multiple factors like storage load, connection, firmware level, raid configuration, access methods and more, it is recommended to do a Proof of Concept to define optimal configuration and the best possible processing mode.

Considerations and Limitations

Remember that several factors can negatively affect backup resource consumption and speed:

  • Compression level - It is not recommended to set it to "High" (as it needs 2 CPU Cores per proxy task) or to Extreme (which needs a lot of CPU power but provides only 2-10% additional space saving). However, if you have a lot of free CPU ressources during the backup time window, you can consider to use "High" compression mode.

  • Block Size - The smaller the block size, the more RAM is needed for deduplication. For example, you will see a increase in RAM consumption when using "LAN" mode compared to Local target, and even higher RAM load (2-4 times) when using "WAN". Best practice for most environments is to use default job settings ("Local" for backup jobs and "LAN" for replication jobs) where another is not mentioned in the documentation or this guide for specific cases.

  • Antivirus - see the corresponding KB for the complete list of paths that need to be excluded from antivirus scanning

  • 3rd party applications – it is not recommended to use an application server as a backup proxy.

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