Home > Windows Server 2003 / 2008, Windows XP / 7 > DFS mapping error: Refers to a location that is unavailable

DFS mapping error: Refers to a location that is unavailable

Last week I experienced some strange behaviors with offline files in combination with DFS. In most environments is DFS really common and used for network mappings, roaming profile, homedrive,.. .

The initial issue was that users experienced random access issues to DFS mappings which solved themselves after some time.

Users get an error like: Drive x refers to a location that is unavailable. It could be on a hard drive on this computer, or on a network. Check to make sure that the disk is properly inserted, or that you are connected to the Internet or your network, and then try again. If it still cannot be located, the information might have been moved to a different location.

DFS_Error

In the beginning I thought that this was an issue with one of the DFS Namespace servers. Mostly are random access denied issues caused due a permission difference on one of the DFS roots.

When the issue occurred I started trying to access the DFS share through different locations:

  • client could not connect to “\\domain.com\dfsroot”
  • client could connect to “\\domain\dfsroot”
  • client could connect to “\\DCA\dfsroot”
  • client could connect to “\\DCB\dfsroot”

Apparently only the “\\Domain.com\” was not accessible. So I also enabled show hidden files and protected files and then I saw that only the Homedrive of the user was available because this was made offline. But what I really found strange was that “\\domain\dfsroot” was just working. I discovered that on desktops the access issue was not happening because offline files were not enabled on the desktops.

After some research on the Internet that Offline Files does not distinguish DFS paths from UNC paths:  Technet blog

So what happens on Windows 7 client: Offline files sync in the background and there is by default a slow-link detection mechanism.

  • If the offline file feature discovers that the network is slow it will work offline (Slow-Link mode)
  • Offline file feature thinks that \\domain.com is the fileserver so it will break the communication to \\domain.com
  • All other DFS mappings based on \\domain.com become unavailable
  • The DFS mappings will become online again if the offline file feature detects fast network again

There is not really a nice solution for this but here are some possible solutions:

  • Disable Slow-Link mode via Group Policies (it will not solve mapping issue when the client really lose it’s connection for a short time)
  • Use UNC paths as network mappings
  • Map network drives as \\Domain\dfsroot (A bit cheating with DFS : so without .com)

I don’t know yet if the offline file feature on Win8/Server 2012 can work with DFS paths.

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  1. Paul
    March 14, 2013 at 11:35 am

    Just came across your post whilst searching google for something unrelated – I had something similar at work. I think I managed to mainly resolve this issue with a couple of hotfixes, and looking at DFS path latency settings for different parts:

    We ended up looking at hotfixes: KB2663418 and KB2705233 and KB2561708

    These may or may not now be in the new rollup – http://support.microsoft.com/kb/2775511 .

    Whilst i’ve not read your whole post, I think our problem with very similar and hasn’t been so bad recently – I’ve left my email address in case you would like me to look back at exactly what we did / were having

  2. Joris
    March 14, 2013 at 3:15 pm

    Paul Very interesting Hotfixes. Thanks for sharing this information!

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