I am curious about your opinion here on btrfs and raid support on the backup NAS unit.
Sure, the
DS120j is perfect for putting away data. But what about disk failure or bit rot? I guess you'd also want to protect your backup.
This pov comes up frequently on NAS forums and related...'yes, but what will backup the backup...?'
My take on it is that the Q subtly conflates 2 different things -
backups and
archives; and I think that when some people talk about
backups they're really talking about an
archive.
The difference is this; an
archive is data that will stay in a relatively cold state, but that nevertheless contains important stuff that must be stored for a long time. Eg, tax records / copies of receipts / old photos of family moments taken years ago / previous versions of an ever-changing or developing project like your plan for world domination... Although rarely (never?) accessed, this stuff must be protected from corruption ('bit rot') because it is fairly irreplaceable if lost.
This stuff is NOT a backup, and as its irreplaceable should be as proteced from corruption and backed up as thoroughly as 'hotter' more current data like my current projects and this years' invoices. BTRS / ZFS, multiple versioning, 3-2-1 rule, all that good stuff applies here.
A
backup is just that. It's something that I only expect to have to use in the event that the primary data is lost. It's something that can be (should be?) replaced frequently so that it is up to date. It should be able to be wiped without much thought and replaced with another, more recent version. I don't need to keep multiple versions going back in time; as long as I have a reasonably recent up to date version that's enough. I don't rely on my backups to dig out old copies of important documents, photos or anything important.
I dont worry about making backups of backups. They're ephemeral, recent (hopefully) and disposable. I only need them in the event that I've deleted something important or a drive has died; and the chances of this happening to both my primary storage and the backup medium at the same time is one I'm prepared to live with. The disk image I make of my machine, the .tar archives or the TimeMachine backups on my mac; these are backups and they can be wiped and restarted again without any worry about loss of data.
For me, separating these 2 things out helped clarify the conundrum of 'yes, but what about a backup of the backup, just in case...'