Tips & Tweaks for Windows

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Copy files on slow links

Since Windows Vista Microsoft has seen the light and made robocopy.exe a part of the standard installation (it was a resourcekit tool before). One of my favourite features is /IPG or Inter Packet Gap. 

Especially when you flooded a network before, you will appreciate this feature. It will prevent that by splitting the data in 64Kb packets and add a pauze in between. The time of the pause in milliseconds is what you define by /IPG. 


This example copies a folder to a network location using an Inter Packet Gap of 100 milliseconds.


Because the best value depens on your network capacity and usage, it's hard to predict the best value.  

For a 2Mbit/sec network connection I recommend to start with /ipg:500. If this succeeds, you might decrease the value. 

The graph shows the network usage of a 100MB copy using robocopy /IPG:500 and /IPG:100. You can clearly see that the first copy uses less bandwith but also takes longer to finish. 

The delay is calculated in the formula: 

[filesize] / 64KB * IPG 

A 300MB file and an IPG value of 500 means a delay of: 

300MB / 64KB * 500ms = 307200KB / 64KB * 0,5sec = 2400 sec = 40 min. 

Check Robocopy IPG Calculator on this site.


I copy a 300MB file over a 1MBit/sec line. If all bandwith is available this will take 40 minutes; 1Mbit/sec = 1/8MB/Sec = 300MB/2400sec = 300MB/40min 

We saw earlier that the delay on this file when using /IPG:500 will also take 40 minutes. This means that during 80 minutes, the job will be copying half of the total time and waiting the other half (leaving bandwidth for other data). 

In my opinion, 1:20 hour is acceptable to deploy a Windows Servicepack. 

This post applies to: Windows 2003, Windows 2008, Windows 2012, Windows XP, Windows Vista, Windows 7, Windows 8.


Tips & Tweaks for Windows

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