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.

As others said, depends on your use case. There are lots of good discussions here about mirroring vs single disks, different vendors, etc. Some backup systems may want you to have a large filesystem available that would not be otherwise attainable without a RAID 5/6.

Enterprise backups tend to fall along the recommendation called 3-2-1:

• 3 copies of the data, of which
• 2 are backups, and
• 1 is off-site (and preferably offline)

On my home system, I have 3-2-0 for most data and 4-3-0 for my most important virtual machines. My home system doesn’t have an off-site, but I do have two external hard drives connected to my NAS.

• All devices are backed up to the NAS for fast recovery access between 1w and 24h RPO
• The NAS backs up various parts of itself to the external hard drives every 24h
  • Data is split up by role and convenience factor - just putting stuff together like Tetris pieces, spreading out the NAS between the two drives
  • The most critical data for me to have first during a recovery is backed up to BOTH external disks
• Coincidentally, both drives happen to be from different vendors, but I didn’t initially plan it that way, the Seagate drive was a gift and the WD drive was on sale

Story time

I had one of my two backup drives fail a few months ago. Literally actually nothing of value was lost, just went down to the electronics shop and bought a bigger drive from the same vendor (preserving the one on each vendor approach). Reformatted the disk, recreated the backup job, then ran the first transfer. Pretty much not a big deal, all the data was still in 2 other places - the source itself, and the NAS primary array.

The most important thing to determine about a backup when you plan one - think about how much the data is valuable to you. That’s how much you might be willing to spend on keeping that data safe.

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).

So many people didn’t read the post and going off how raid isn’t backup.

There are a few things to consider. How much data is it? How is it connected? How reliable do you want it to be? Where is it going to be? How are you backing it up? How will you monitor the disk(s) and backup process for failures?

Is it at some place that will be a pain to deal with if a hard drive dies, like a friend’s house or something. I’d deal with raid so it wouldn’t be an immediate reason to go fix it or go without backups.

Is it small enough amounts of data that you could have a complete third copy if you didn’t put the disks in raid? Then I’d probably make multiple copies and not use raid.

Are you dealing with something like veeam doing backup chains? Having an initial copy and then incremental with changes where you can go back to different days? Go with raid because having to reconfigure can be a hassle or having a full and incremental across jbods could cost you all the backups if the disk with the full backup is lost.

Either or is a valid choice and depends on your particular needs.

Snapraid to a single drive works well if you are fine with daily snapshots of up to 6 drives.

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

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

RAID is a choice if you’re (generally) trying to maximize storage capacity against cost of drive capacity. It was born out of a lack of drives of sufficient capacity.

Mirroring is useful for protection against hardware failures - it’s not a backup.

Follow the 3:3 rule: 3 backups, in 3 different “locations”. Locations in quotes because 2 different cloud storage providers count as 2 different locations.

Whether your “local” backup (in your location, at a friend’s house, etc) uses RAID depends on your requirements, cost sensitivity, etc.

I have a couple RAID setups only because I always have spare drives around, and it’s relatively cheap to build a box to run something like UnRAID or TrueNAS which can take advantage of mixed drive sizes.

My current setup is an old file server with a large drive that is currently replicating to an external drive, a small NAS, and Crashplan.

Not an ideal setup since 2 backups are local (though my NAS is easy to grab and run with, weighs about 10lbs).

Next phase is to move to Storj.io and switch to a proper backup tool like Borg.

Any storage shut be raid or a form their of in a ideal world. The storage where backups are stored a defiantly yes raid shut be a very high priority.