June 19, 2013

SharePoint Downloads Interrupted for Large Files

While we primarily use SharePoint Online (2013) for fairly small documents - the largest are still less than 5MB - I recently decided to start uploaded recorded team meetings from Lync 2013. The videos are about 30 minutes in length and end up being around 40-60MB in size. Although the upload runs fine, users were reporting issues when trying to stream the files or attempting to download it. The stream would simply stop and the downloads fail with a message that the download was "Interrupted". We replicated this behavior across 4 different locations with the same result - at some random point in the download, it would fail.

The only location where it seemed to work just fine was at our datacenter colo, which enjoys a snappy 1Gbps connection. The slower the internet connection at our local office though, the more likely the download was the get interrupted.

While Microsoft continually referred to this as "network issues" on our end, that just wasn't the case. From any other site (even SkyDrive), large downloads work flawlessly, and these downloads from SharePoint consistently fail.

The workaround was to disable TCP Auto Tuning on our machines by opening an administrator command prompt and entering the following:

netsh int tcp set global autotuninglevel=disabled

Auto Tuning is a feature that scales the TCP window dynamically. You can read more at this KB article: http://support.microsoft.com/kb/947239

The takeaway from that article is the following paragraph:
"If you enable Receive Window Auto-Tuning for WinHTTP traffic, data transfers over the network may be more efficient. However, in some cases you might experience slower data transfers or loss of connectivity if your network uses an older router and firewall that does not support this feature. For example, when you use Windows Internet Explorer to access applications that are hosted in Microsoft Office SharePoint Server, the HTTP traffic may slow down. This occurs because certain routers do not support the Receive Window Auto-Tuning feature."
Hopefully this is something that will be addressed in a future release/update of SharePoint Online, but as of 6/19/2013 it is still an issue for us.


  1. Thank you for this, worked like a charm. We started to experience this issue on SharePoint Online just a couple weeks ago so I also hope this is addressed sometime soon.

  2. I have to admit...I gave this like 1% chance of working. Sounded like voodoo! but BAM! Fixed my problems and I love you.

  3. I was looking all over for a solution, finally came across your site! works like a charm! thanks for sharing.

  4. Well how about that - it actually works.

    On the other hand, I've got a new, top of the line router. I'm fairly certain it supports, like, everything. I could be wrong because this is somewhat outside my area of expertise, but since this only impacts large downloads from Sharepoint (as opposed to GDrive, OneDrive, Dropbox, etc.) I suspect the issue isn't on my side...Microsoft, are you listening?

  5. Thanks Paul. It works like a charm.