The drive is mirrored by the OS.
This protects against hardware failure of your online copy.
E.g. you're storing data on disk 1, this is automatically backed up to disk 2,
if disk 1 fails you still have disk 2 available.
BUT, if you delete the file on disk 1, or you get some virus that corrupts files on disk 1, the changes are automatically copied to disk 2, (including delete or corrupts).
it doesn't add additional chances for data corruption, the point is that it's not a backup tool to guard against data loss, it's a method to keep an online copy in the event of hardware failure. (e.g. you still have access to your files. even if 1 hard drive breaks)
it's a single online copy, it's considered 1 copy for the "enterprise level" that you are talking about.
backing up that drive to your NAS and then to your external hard drive sounds good, but how are you doing this?
if you're synchronizing data at a given time, does that include synchronizing delete events? and corruption?
e.g. are you synchronizing all changes and overwriting the backup data. - if your files have become corrupted that may include a change in the modified date. if you got that virus that encrypts all files, that definitely includes the modified date changing, so you may write over your good copy on NAS before you even realize that your local copy is bad?
same how you copy to external HDD...
of course it all depends on the method of how you make your copy...
Then you have the issue that all your files are in one location, so in the event your house burns down then all your copies are lost.
I didn’t fight my way to the top of the food chain to be a vegetarian…
Im sick of people saying 'dont waste paper'. If trees wanted to live, they'd all carry guns.
"The inherent vice of capitalism is the unequal sharing of blessings; The inherent vice of socialism is the equal sharing of miseries."