Understanding bandwidth throttling for backup

Ian Waters

Bandwidth throttling is an important tool for backup as it enables you to limit the amount of available bandwidth your backup system will use during a set period of time. Typically, this will be during normal working hours when the network is under heaviest use. Without bandwidth throttling, your backup system will attempt to use all of the available bandwidth the network or device being backed up is capable of supplying – this will obviously slow down critical business systems if during working hours. It’s important to remember that the limitation to bandwidth may not just be the internet connection, but could also be the device’s link speed, for example if a device (laptop or pc) connects over wireless.

Should I use it?

Any system that will attempt to utilise all available bandwidth will likely cause issues at some point. In the case of offsite backups this will usually be during the first initial backup, which depending on the speed of the connection, could be anything from a few minutes to several days. Unless you have an abundance of upload bandwidth available then you should definitely have a limitation in place. If you’re already pushing the limits of your internet connection, then configuring an offsite backup solution could cause an upload bottleneck resulting in lower download speeds.

Calculating available bandwidth during working hours

A quick way to gauge your available bandwidth is to run a speed test. There are plenty of speed test sites available, but I use www.speedtest.net. Just remember this only gives you a snap shot of what speeds are attainable at that point in time, but it can give you some initial figures to work with. If you have a router with a bandwidth monitoring feature, you should use that to get more accurate results where possible. Running the test on your network at various points during the day will give you an idea of usage and available bandwidth. On our own network each test reported upload speeds of 17Mbps. Since we’re uploading data we don’t need to concern ourselves with the download. So we can use this average upload speed to calculate how long our initial and delta backup data is going to take to transfer offsite.

Estimated backup transfer size (seed) and calculate time to upload

Without any estimation tools we need to assume the worst case scenario, which is that all of our data is already compressed so the initial backup size will be the size of the backup selection. In reality it’s going to me much less but without any tools it’s always beneficial to assume the worst. 

From here, we then take the initial size of the backup to be transferred offsite and we can calculate the time required to upload it. We can use a file transfer calculator like the Cloud Calculator and enter the available upload speed and the size of the initial backup and it will give us the estimated time to upload the backup.


For example, uploading an initial backup size of 500GB with an upload speed of 17Mbps will take an estimated 2 days 22 hours and 10 minutes. This is quick but even if it’s started over the weekend the upload will run over into Monday morning when everyone comes into the office. As a managed service provider (MSP) you need to take into account that not all customers have the luxury of fast broadband, so it’s likely to take much longer.

User complaints

Leaving a backup uncapped will cause it to utilise all of the available bandwidth, which for businesses with limited broadband speeds will cause major problems. Reports of slow internet, emails taking a long time to update and OneDrive taking longer than normal to update are bound to make their way into support tickets.

The solution

To prevent backups having any noticeable impact on users, you need to enable bandwidth throttling and avoid all of these problems. The backup may take a little longer to upload but the throttling only applies on selected days and during a selected period of time in the day. So the backup can run unrestricted all weekend and evenings but when the users come into work it gets throttled back to your set limit. Deciding how much to throttle the bandwidth depends on your bandwidth speed tests, but I will usually set throttling between 25% and 50% of the available bandwidth as a starting point. If there’s no issues reported, you can always decrease the throttling later to speed up the incremental backup uploads.

How to enable bandwidth throttling in MAX Backup

It’s so easy to enable bandwidth throttling in MAX Backup, and it resolves so many issues that it should always be enabled. Simply log into the backup manager, click on the Preferences tab then click Performance. 

  1. Tick the box to enable bandwidth limiting. 
  2. Set the time you want the throttling to apply and set your desired limits. Here we limit the upload to 5Mbps between 6am and 7pm. 
  3. If desired set specific days where no bandwidth throttling will be applied. Here we set unrestricted throttling on Saturday and Sunday.
  4. Press Save to finish.


Offsite backups are vital to protecting business data and make up a large part of an organization’s disaster recovery plan. Implementing MAX Backup is easy, but unless you have an abundance of bandwidth you must implement bandwidth throttling for a successful install.