By combining multiple technologies such as network compression, multi-threading, dynamic TCP window size, variable block size deduplication and global caching, WAN acceleration provides increased transport speed for Backup Copy and Replication jobs on low bandwidth or limited network links. This technology is specifically designed to accelerate Veeam jobs. Any other WAN acceleration technology should be disabled for Veeam traffic.
WAN accelerators work in pairs: one WAN accelerator is deployed at the source site and another at the target site. Many to one scenario (e.g. ROBO-sites to a central DC) is also possible but needs accurate sizing and has higher system requirements.
How many source WAN accelerators do I need ?
Since WAN accelerator processes VM disks sequentially, you may consider using more than one source WAN accelerator on a single site to distribute tasks between them. Many-to-one scenario is supported but the target WAN accelerator should be sized carefully in this case with recommended ratio 4:1.
The source WAN accelerator consumes a high amount of CPU and memory whilst re-applying the WAN optimized compression algorithm. Recommended system configuration is 4 CPU cores and 8 GB RAM.
When you are using the WAN accelerator server also for other Veeam roles like Proxy or Repository make sure not to overcommit CPU and memory resources and there are enough resources for each role.
The I/O requirements for the source WAN accelerator spikes every time a new VM disk starts processing, so the typical I/O pattern is made of many small blocks. Thus, it is recommended to deploy WAN accelerators on disk configurations with decent I/O performance, avoiding high latency spinning disks.
Source WAN accelerator IOPS
Source WAN accelerator stores only the digests of the processed VM OS data blocks in the VeeamWAN folder on the disk that you select when you configure the WAN accelerator. Disk digest file is created and placed in *\VeeamWAN\Digests<JobId>_
Each digest file consumes up to 2% of its source VM disk size. VM disk size is calculated based on the allocated space, not used space. This means, for example, that a 2 TB VM disk file can produce a single set of digest files up to 40 GB in size.
WAN accelerator keeps 2 copies of digest files for each processed VM disk resulting from the previous session and current session. At the end of the session these 2 files are merged into 1. As we need to count for this, we will calculate 5% of source VM Disk size for digest files. Additionally, plan for 10 GB of working space for payloads and other temporary files.
o Formula: Digests = (Source data size in GB) * 5% + 10 GB o Example: with 2 TB source data: (2,000 GB * 5 %)+ 10 GB = 110 GB
Note: The cache size setting on the source WAN accelerator will always be ignored, the digest files will be produced regardless of cache size setting configured. They may consume considerable disk space. Even if configuring the cache size on a source WAN accelerator is not as important, it still must exist as a number. Another folder created on the source WAN accelerator is VeeamWAN\GlobalCache\src. The only file created in this directory is data.veeamdrf file. This file will be synchronized from the target WAN accelerator in following cases:
• Source WAN Accelerator cache was manually cleared, or digests deleted
• There was not enough space on the source WAN accelerator
• It is the first session after enabling the WAN accelerator setting
• If the job was seeded/mapped
The size of this file is typically up to 2% of the configured target cache size (see sizing target WAN); thus, it may take some time for the initial data transfer to begin
o Formula: data.veeamdrf = TargetCacheSize * 2%
The following recommendations apply to configuring a target WAN accelerator.
• The cache size setting configured on the target WAN accelerator will be applied per connected source WAN accelerator. This should be taken into account when sizing for many-to-one scenarios, as configuring 100 GB cache size will result in 100 GB multiplied by the number of source-connections configured for each target WAN accelerator.
• It is recommended to configure the cache size at 10 GB for each unique operating system processed by the WAN accelerator.
Note Each version of Microsoft Windows OS is considered to be unique, while all Linux distributions are treated as one OS.
Although a target WAN accelerator consumes less CPU resources than the source, the I/O requirements for the target side are higher. For each processed data block, the WAN accelerator will update the cache file (if required), or it may retrieve the data block from the target repository (if possible). The cache is active on operating system blocks only, while other data blocks are being processed only with the WAN optimized data reduction algorithm.
Target WAN accelerator IOPS
Tests show that there are no significant performance differences in using spinning disk drives as storage for the target WAN accelerator cache rather than flash storage. However, when multiple source WAN accelerators are connected to a single target WAN accelerator (many-to-one deployment), it is recommended to use SSD or equivalent storage for the target cache, as the I/O is now the sum of all the difference sources.
Ensure that sufficient space has been allocated for global cache on the target WAN accelerator. At least 10 GB per each different OS that is backed up. That is, if you plan to backup VMs running Windows 10, Windows 2016, Windows 2019 and RHEL 8 (four different operating systems), you will need at least 10 GB * 4 = 40 GB Plan for additional 20 GB of working space for cache population, payload and other temporary files. If the cache is pre-populated, an additional temporary cache is created. The temporary cache will be converted into being the cache used for the first connected source. Subsequently connected sources will duplicate the cache of the first pair. As caches are duplicated the configured cache size is considered per pair of WAN accelerators.
• Formula for configured cache size (insert this number in configuration wizard):
o (Number of operating systems * 10 GB) + 20 GB
• Formula for used disk space (Many-to-one scenario)
o (Number of sources * <formula for configured cache size>)
• Example with one source and two operating systems:
o Configured cache size: (2 operating systems * 10 GB) + 20 GB = 40 GB o Used disk space: (1 source * 40 GB) = 40 GB
• Example with five sources and four operating systems:
o Configured cache size: (4 operating systems * 10 GB) + 20 GB = 60 GB o Used disk space: (5 sources * 60 GB) = 300 GB
In some cases space for digest data is also required on the target WAN accelerator. These cases include a manually clear cache operation on the source WAN accelerator, a corrupted digest file or other operations which require a re-calculation of the digest cache.
In these cases the digest will be re-calculated from the target side data and the calculated digest file - which is 2% of the source data - will be transferred to the source WAN accelerator.
If the required 2% of source data is not available on the target side WAN accelerator the transport will continue in the limited mode which will not do any more deduplication.
• Example with 2TB of source data
o 2TB source * 2% = 40GB digest data
• Example with 5 sources each 2TB of source data
o 5 * 2TB source * 2% = 5 * 40GB = 200 GB digest space
For understanding how the disk space is consumed, please see the following sections.
For each pair there will be a subfolder in the trg directory, with a UUID describing which source WAN accelerator the cache is attached to. In each of those subfolders, the blob.bin file containing the cache will be located. That file size corresponds to the setting configured in the management console. Note: The blob.bin file will exist for all connected source WAN accelerators.
When connecting a new source WAN accelerator, the temp folder will temporarily contain the data.veeamdrf file that is later transferred to the source containing the cache manifest.