We need to clear up the SQL Server versus MySQL confusion. They’re completely different databases. SQL Server seems to have good VSS support. http://projectinabox.org.uk talks about SQL Server but not MySQL.
CrashPlan is a file-oriented product that can use VSS (Duplicati is also), and such a plan has inherent limits:
Back up open files and databases
Understand and troubleshoot backing up open files with Windows VSS
The above has links to explanations. Here’s another:
Crash-Consistent vs. Application-Consistent Backup
SQL Writer Service desribes the component of SQL Server that lets it better support backups that use VSS.
MSSQL backup how’s it work exactly? is some Duplicati-specific discussion, with a specific SQL Server plan. This discussion says how Duplicati asks the database engine to create an application-consistent snapshot, however it’s probably basically the same thing that any backup using VSS would do. See the above articles. Basically, it looks like getting the application-consistent backup needs VSS, and also some application help.
MS SQL does not backup modified files is likely why --disable-filetime-check is used in detailed steps above.
Successfully piecing together a system (or even an application) from a collection of files seems challenging. Don’t you want to carefully reinstall pieces out of the file backup, or does it really work to just install all of it?
I have little personal experience with live image or high-cost backups, but some image backups do use VSS, possibly giving a backup that’s not quite as “best practice” as database dumps, but offers other advantages.
Backup Internals: What is VSS, how does it work and why do we use it?