I disagree - to a point.
I agree that a snapshot is NOT a backup. However, a backup that is taken that is based upon a snapshot is perfectly reliable.
Before a snapshot is taken, Windows stops all data from being written to the ACTIVE filesystem and flushes any writes that are in flight to give you a consistent point in time. Only then is the snapshot taken and the backup is then in turn based upon the contents of the snapshot which remain consistent and do not change during the entire duration of the backup.
I'm giving the highly simplified version here, because there is actually a lot more involved. For databases, mail servers, etc., those types of programs are VSS aware and take special actions when VSS is preparing to take a snapshot so that those applications can guarantee consistency down to the individual transaction, but that's a complicated topic that we don't need to go into here.
So, while a snapshot is not a backup by itself, a snapshot can allow you to create a reliable, consistent snapshot.
Please be aware that I am making the assumption that everything is working properly. As with everything else, things can break. But then again, things can break even if you are doing a backup where the OS is not even running. Nothing is perfect
Yes, a backup that is based upon a snapshot is perfectly reliable, just not in the particular sense that, after the restore, problems can not occur as a result of data partially gone missing during the backup process. The part of the data that goes missing is the part that, AFTER the point in time that you are referring to here, gets written to the volume by those specific tasks that lack the ability to be made aware of the fact that a snapshot of this volume is about to be taken.
One reason why I don't need to go into the complicated topic of
application-consistent snapshots here is
exactly because I shut down Windows before I make an image of the partition that Windows has been installed on. Neither the bootable ISO of Acronis nor the bootable ISO of Macrium will alter the data stored on that partition after I boot into that ISO with Ventoy, excepting only if I use that ISO to purposefully mess with that partition of course, but then, I am too lazy to even try to mess with it, so... until the verification finished OK, that partition is going to stay 100% unaltered. Of if the SSD fails in such a way that it is what causes that partition to still be altered, then it will be extremely unlikely that the verification will still finish OK, as read errors going twice undetected are rare like unicorns. (Maybe even rarer than that.)
The other reason why I don't need to go into that topic here is because it plays a fairly important role in what I do for a living as an Enterprise Java developer, and I like to keep all my Windows related hobbies almost completely separate from all my work related stuff. So, I will only add that, while it certainly is true that inconsistencies are
not always problematic in the particular sense that they cannot safely be ignored, they still
can be problematic in that particular sense.
The fact that Windows stops all data from being written in such a way that any chunk of data that still needed to be written will be absent after the restore because it will be absent from the actual backup itself, and stops it regardless of whether a task has the ability to recover from an inconsistency that results from this absence is one obvious example of why that is, and, if the OS is not even running, then logically, neither are those specific tasks that could potentially create the kind of inconsistencies that turn out to be problematic after it will be already too late.
Shutting down Windows to boot straight into a bootable ISO that is stored on a Ventoy-formatted USB flash drive to make an additional new incremental image a few times per year doesn't take too much extra effort, even for someone who is lazy like me. In addition to the other advantages that I already mentioned in my first reply to this thread, what I get in return is the kind of verification that happens to be a lot less imperfect than this
other kind of verification that primarily exists within people's rampant imagination.
