I would also like to point out, since no-one else has, that the way you
CONFIGURE a NAS, or backup software, has a major influence on how secure it is.
For example, if your controller malfunctions, and writes corrupt data to your backup drive or NAS, then the damage is already done.
And, depending on the situation, you may never know it until you go to read that backup someday.
That's why it always pays to check that "verify" box on your backup software (or your CD/DVD/Blu-Ray burner).
When you do that, after the data is written, it is all read back and compared to the original.
It takes twice as long, but you
WILL be notified if your backup isn't perfect, sooner rather than later.
And, if you have really valuable files, it makes sense to use some sort of checksum software.
You may not really be able to see if a few bits on a 10 gB video have gotten flipped - depending on where they are.
But, if you calculate a checksum of that file, you can use it later to verify that the file is
EXACTLY the same as it was before.
When you verify a backup the data is read and compared to the original - but you can only do that if the original is still there.
A checksum stores a form of "digital signature" of each file, which you can use to confirm that it has remained unchanged, even without the original.
Even though the checksum is relatively small compared to the file, it can confirm that the original remains unchanged with great certainty.
(A simple checksum won't enable you to fix a damaged file - but it will warn you so you can go find your backup copy and take steps to fix the problem.)
In a typical usage scenario you might store a checksum in each music folder on your server.
Then, by simply issuing a command to "check all folder contents against their checksums", the entire drive can be confirmed to remain exactly as it was originally - or not.
(And, if you think you've heard a problem, you can quickly confirm that the song you were just listening to hasn't gotten corrupted.)
