Sharepoint 2010 VSS Writer returns components with type VSS_CT_DATABASES only

[Sergey]

Hello
I am working on backup software for Sharepoint.
Have checked returned components for Sharepoint 2010 VSS Writer
with command "diskshadow list writers"
But returned components are VSS_CT_DATABASES only ( associated MS SQL
databases )
Is it normal?
How can I get VSS_CT_FILEGROUP type components for Sharepoint from it
writer? ( to know which files in shadow copy to backup)
My configuration is:
1.Standalone configuration of sharepoint 2010 (sp1 applied) server
is running on server 2008R2
2. Volume Shadow Copy and SharePoint 2010 VSS Writer services is
running
3.Sharepoint VSS Writer was registered in system ( " STSADM -o
registerwsswriter ")
4.SharePoint 2010 VSS Writer is running as Network Service
5.In registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\VSS
\VssAccessControl
keys :
NT AUTHORITY\LOCAL SERVICE 1
NT AUTHORITY\NETWORK SERVICE 1
Thanks