Depending on your age and taste in music, you may recognize “Low Spark” as the title of a popular song by the band Traffic. But you don’t need to be a fan of classic rock to appreciate how traffic impacts the performance of offsite data synchronization, which is the subject of this article.
The synchronization of change data between an Axcient appliance and the Axcient cloud involves periods of sustained traffic flow. This would ordinarily consume available bandwidth to move data offsite as quickly as possible. However, if “traffic shaping” is being employed along the path between the appliance and the data center, offsite backup performance may degrade considerably.
Traffic shaping (also called packet shaping or bandwidth throttling) is an automated technique for managing bandwidth by regulating the flow of certain data. Traffic shaping is evident when the throughput of sustained traffic starts at a high rate for a short period of time and then suddenly declines. For example, an Axcient client site recently exhibited an initial throughput of 4 megabytes/second that was being throttled down to 69 kilobytes/second when a mere 20 megabytes of data was being transmitted. That’s 98% performance degradation!
Firewalls and routers can be configured to automatically throttle down throughput when sustained traffic flow is detected. Sometimes these devices are configured for traffic shaping by default without the user realizing it. Internet service providers may also employ traffic shaping policies and even block an IP address when a certain amount of sustained data flow is observed.
If your offsite backups appear to be running slow for the amount of change data and available bandwidth you have, there’s a simple test to determine whether traffic shaping is the problem. The idea is to upload a small amount of data from the Axcient appliance to the Axcient data center and observe the throughput. Then upload a larger amount of data and observe again.
To facilitate this test, the network utilities in the Axcient appliance UI have been expanded as of the 2.11 release. Specifically, the Offsite Bandwidth Check lets you specify the amount of data to upload to the Axcient data center for measuring throughput. (Since you’re testing for traffic shaping, don’t select the option to “use current QoS”, which would activate appliance-imposed bandwidth throttling.)
Using the Offsite Bandwidth Check, first upload a small amount of data (2 MB) and note the data rate reported in the UI. Then do the same for a larger amount of data (32 MB). The results should be interpreted as follows:
- If the throughput is about the same for the small amount of data and the larger amount, then there is no traffic shaping
- If the throughput for the small amount of data is considerably greater than that for the larger amount of data, then traffic shaping is likely impeding your offsite backup
This simple test should help uncover when traffic shaping is at play. You can then take corrective actions to ensure smooth traffic flow and faster offsite backups.
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