It's too bad Unix/Linux doesn't offer something like Windows' VSS API, where the operating system can inform registered applications or services of an impending backup operation.
It's too bad that VSS is unreliable. If I had a nickel for everytime one of my backups failed due to a VSS writer issue, I'd own Symantec AND EMC. This has been across Win2k/2003/2008. We've been using 2012 for the last year (yeah, old stodgy corporations move slowly), and I haven't seen the same number of errors, but we're also not doing as many client based backups either.
Have you guys thought about giving Windows ZFS volumes over iSCSI and then take ZFS snapshots? For example with SQL Server, it should be possible to talk to the SQL Writer Service and create a consistent database snapshot of a live SQL Server database with ZFS.
When this snapshot is taken you can send & recv the diff to a remote backup server.
Our experience with iSCSI hasn't been very good; its use is limited to some dev ESX systems. Our DBAs prefer to perform cold backups that we backup with traditional tools (Avamar).
