KB: WDS installation images fail and are deleted when configured for multicast in System Center Configuration Manager 2007

Consider the following scenario:

1. You are using Windows Deployment Services in System Center Configuration Manager 2007 (ConfigMgr).

2. You are configured to use multicast.

3. You are deploying sparse files as part of your deployment.

In this scenario we see that some installation images get downloaded as sparse files. Because the initial hash is computed before the files are made sparse and the verification hash afterwards, both hashes are different. This leads to the deletion of the image and the failure of the install.

When you run into this problem will also see entries similar of the following in the SMSts.log file:

Found sparse part of the file: 5236588544 8192
File not processed completely. Partial results may exist.
Completed Extract File Succesfully
Download done setting progress bar to 100
Succesfully performed multicast download from mcs://<fqdn>/SMS_MCS/.sms_mcs?filePath=\\<fqdn>\SMSPKGD$\C0100978\&PackageFlags=134217728&packageID=C0100978&version=1
Hash could not be matched for the downloded content. Original ContentHash = ADB7A269FA5A45685BB67C7CFC933BB6D5A76D27, Downloaded ContentHash = 1F1748813C696136E1937A003115D70256015FB5
0L == TS::Utility::VerifyPackageHash(pszContentID, sDestination), HRESULT=80091007 (c:\qfe\nts_sms_fre\sms\framework\tscore\resolvesource.cpp,2903)

In a pure WDS environment you can use wdsmcast.exe /usesparsefile:no to work around the problem. In ConfigMgr, currently the only option is to use unicast (i.e. disable multicast).

For more information on how multicast is enabled/disabled, see the following:

How to Enable Multicast for Operating System Deployment : http://technet.microsoft.com/en-us/library/cc161854.aspx