2 Single drives means 2 full copies, one you can keep at a friends place. 2 mirrored drives means if you accidentally overwrite a backup, you have lost both drives to the error, unless you have snapshotting or imcremental backups.

Lots of good backup advice on this podcast https://2.5admins.com/

Generally speaking, fault protection schemes need only account for one fault at a time, unless you’re a really large business, or some other entity with extra-stringent data protection requirements.

RAID protects against drive failure faults. Backups protect against drive failure faults as well, but also things like accidental deletions or overwrites of data.

In order for RAID on backups to make sense, when you already have RAID on your main storage, you’d have to consider drive failures and other data loss to be likely to occur simultaneously. I.E. RAID on your backups only protects you from drive failure occurring WHILE you’re trying to restore a backup. Or maybe more generally, WHILE that backup is in use, say, if you have a legal requirement that you must keep a history of all your data for X years or something (I would argue data like this shouldn’t be classified as backups, though).

I would go with raid on the backup system too. you don’t want all your backups disappearing because one drive fails.

It depends on your needs. How much do you value your data? Can you re-create / re-download it in case of a disk failure?

In some case, like a typical home users with a few writes per day or even week simply having a second disk that is updated every day with rsync may be a better choice. Consider that if you’re two mechanical disks spinning 24h7 they’ll most likely fail at the same time (or during a RAID rebuild) and you’ll end up loosing all your data. Simply having one active disk (shared on the network and spinning) and the other spun down and only turned on once a day with a cron rsync job mean your second disk will last a LOT longer and you’ll be safer.

I use a RAID for the data but the backups go to simple single disks. My reasoning is, I already have a RAID and redundancy. And I don’t have an unlimited budged. It’d already need 2 disks to fail to wreck the RAID and then also the backup has to fail with that solution. That’s probably a fire or ransomware or a deliberate effort. Adding one more disk of redundancy would probably not change much. But It’d cost and add complexity.

Also this way I don’t need to care about buying disks of a certain size and go through painful migration processes more than necessary. I can re-use the drives with mismatched sizes and swap them in to the backup pool.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I’ve seen in this thread:

5 acronyms in this thread; the most compressed thread commented on today has 8 acronyms.

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I have 1 off site and two 10tb external drives that are duplicate backups.

Could always use UNRAID for the backup if you’re trying to be storage efficient, but it’s really no better than RAID5

I have a tiny archive of my own consisting of one 1 TB and one 2 TB USB HDDs by different vendors. Whenever I want to save something, I put it on both. Btrfs snapshots make that really easy.

RAID. No question. Or two individual drives each alternating full backups, which is what I do.

I just plugged in a new drive to replace an SSD that locked and wouldn’t write new backups. It failed a format attempt. I immediately ordered a replacement. Remember the rule: one is none.

And for fucksake, have an offsite backup.

Object storage is really popular for backups now because you can make it immutable by protocol standard and with erasure coding you can have fault tolerance across locations.