Hi Vladimir, thanks for your response. My volume filter driver is registered as Upper Filter for regular Volumes (exposed by legacy volume manager), Snapshots and also to CSV voumes (exposed by CSV Volume manager). I was trying to make sure whether all thes places would cover every paths the write IOs are traversing to volumes which we snapshot using software provider and use it to back it up.
I think you confirmed my logic as if the volumes are Snpashotted (at least one live snapshot) then CSVNSFlt will send the writes to volume stack. SO I think I need to keep my snapshots (or at least one) so that I can keep tracking the writes forwared by CSVNSFlt.