Sizing VMcom? No Problems with this simple guide.  Contact us and we’ll confirm you’ve sized correctly.

Sizing VMcom? No Problems with this simple guide. Contact us and we’ll confirm you’ve sized correctly.

VMcom sizing guide

This article explains how many CPUs, memory and other resources should be allocated to VMcom Backup virtual machine in order to achieve maximum performance and efficiency.

Backup Storage

This guide assumes you already have a backup storage target with appropriate size and performance. For the sake of example, let’s assume your storage target has 20 TB of capacity and maximum throughput of 300 MB/s.

How to size VMcom to match your infrastructure?


VMcom is capable of using multiple backup threads simultaneously to enable parallel processing of virtual machines. Total number of backup threads is limited to:

number of CPUs * 2

If the appliance was assigned e.g. 4 virtual CPU cores, it will utilize up to 8 backup threads.

Note: Users also have the option to further limit thread count of individual backup jobs. This setting allows for job prioritization once a total thread limit has been established.

Backup threads are internally throttled by vSphere to make sure they don’t negatively affect running virtual machines. Performance of a single backup thread is very similar to the performance of a Storage vMotion operation and in most environments defaults to about 30 MB/s.

Considering our example backup storage with 300 MB/s throughput, it should be ideally utilized by 10 backup threads. In this case, VMcom should be assigned 5 CPU cores for best performance.


VMcom’s internal deduplication mechanism is highly effective but requires some amount of RAM in order to work efficiently. A good rule of thumb is:

(1 GB of RAM per each TB of backup storage) + 2 GB of RAM for the appliance

In the case of our example storage with 20 TB of capacity, we’d recommend allocating 22 GB of RAM to VMcom virtual machine.

Deduplication cache (optional)

In order to further increase the throughput of a backup storage, VMcom can utilize fast SSD drives as a caching layer. Determining the size of the cache disk is similar to determining the amount of RAM. VMcom recommends:

10 GB of SSD size per each TB of backup storage

Our example storage has 20 TB of capacity, hence 200 GB of SSD cache is recommended.

Conclusion (TL;DR)

Take a look at the following table to determine the optimal size for your VMcom Backup virtual machine.

Backup storage capacity Recommended RAM Recommended SSD cache size
1 TB 3 GB 10 GB
2 TB 4 GB 20 GB
4 TB 6 GB 40 GB
8 TB 10 GB 80 GB
12 TB 14 GB 120 GB
Concurrent VM backups CPU core count Backup Storage Throughput
1 1 30 MB/s
2 2 60 MB/s
4 3 120 MB/s
8 4 240 MB/s
12 6 360 MB/s