FSDepends Registry Value and it's impact on Backup Exec's functionality
On Windows Server 2008 R2 Standard, I have been trying to create a VM through Hyper-V.
The following error
"A Virtual Disk Provider for the specified file was not found"
was displayed, which has been addressed in the Support article below:
https://support.symantec.com/en_US/article.TECH124353.html
It suggests that the registry key "HKLM\SYSTEM\CurrentControlSet\Services\FsDepends" REG_DWORD value "Start" be changed from "3" to "0" as a solution.
It continues: "When any third-party backup software loads its tape device driver, the software can sometimes result in FSDepends.sys and VHDMP.sys not initializing correctly."
However, before I make the registry change and restart, could someone kindly please explain what the FSDepends.sys does and why Symantec Backup Exec requires the registry value to be set to a value of 3 in the first place? Was there an error in Backup Exec?
Afaik, fsdepends.sys is a mini-filter driver and not directly called / used by Backup Exec. When BE loads its tape driver, it conflicts with fsdepends.sys being loaded as well. By setting the registry key to 0, it allows the fsdepends.sys to load immediately during boot up and thereby avoiding the conflict with the tape drivers. fsdepends.sys actually tracks file system dependencies and i believe either having a read at Windows Internals or checking with MS will provide more details.
Btw, it is originally a MS article and since it affects BE (and other backup software which supports tapes), it has been referenced on the other vendor sites. (I have posted an example link below) And as pkh suggested earlier, if you really would like more detail as to why fsdepends.sys does, then MS is indeed the appropriate place to ask.
Original MS issue - https://support.microsoft.com/en-us/kb/2013544
KB from Appasure which is similar to the BE's one - https://support.software.dell.com/appassure/kb/119790