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Replication Bandwidth Calculator


How many times do you get asked “how do I work out if VM Replication will work with my internet link” Well I wanted to demonstrate some way of providing a calculator without working it out in my head every time. So I made a Replication Calculation tool.  It is assumed that you provide it with 3 values:

  1. Average Rate of Change.
  2. The Link speed – this value should reflect the upload speed at the source site or the download speed at the target if this is less. So for example if the upload at the source is 6Mbs and 10Mbs download at the target then go for 6Mbs
  3. Bandwidth % – which is the amount of bandwidth as % which achievable from the link speed specified.


So how do you work out of the “Average Rate of Change” Well if you are using products like Veeam Backup you can monitor a local backup or replication for a period of time which will give you a good indicator of Rate of Change.

If we look at the properties of a completed backup job:


You can monitor the size of the delta’s (.vbr files) and work out the average.


As you can see from this example the average rate of change is 7.63GB or 7813.12MB

So let’s use a scenario as an example:

The line speed is 6Mb/s and we questimate that we will get 70% of the bandwidth…

Next download and install ReplicaCalc from here >  ReplicaCalc (10261 downloads)


If you cannot perform a local backup/replication to ascertain the average rate of change then you could always use the RateOfChange RuleOfThumb or RCRT which states that overtime on average the rate of change will be ~10%. So if your source full snapshots equate to 1TB then the rate of change will 100Gb. Of course this is BS as every user has different results but it’s a good starting point if you have nothing else to reference.

Note this tool only gives you an approximation. Too many factors can change the actual outcome.

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