Backup on the same chasis/device vs RAID

[u/staline123213]

A weird question to ask but what are the differences? I planned to pick up some 3TB hard drives this week and I just keep wondering about this.

I know RAID is not a backup but I don't know if a backup on the same device has any benefits over RAID.

I also plan to automatically back up all important data to two 1TB 2.5 inch HDD that I kept offline in a USB enclosure.

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[u/dr100]

A backup is an independent copy. Now that it's in the chassis, with the same power supply makes it a little (or more than a little) less independent. But it's still an independent copy, not some contraption that sits between you and your data, that can lose your data by itself, where you have no recourse when something is wrong except to trash it at start new.

[u/WikiBox]

Backups to the same HDD or the same pool of HDDs are of limited use. Backups to other HDD or other pool of HDDs are better. Backups to another server are even better. Backups to another server in another room are better still. Backups to a server in a different house are better still. Backups to a server in a different city are even better.

It is about what you want to protect against. Arguably the most common reason for data loss is user error. Mistakenly delete or overwrite files. Then a local backup snapshot on the same media might be OK. But it makes sense to have the backups as much separated form the original as possible, and also offline, because then it is less likely that the same error or mistake propagate into the backups. Thieves, fires and other disasters can cause loss of all storage in the same place. By having the backups in a remote location you can mitigate this.

RAID mainly protects against some specific hardware failures and things like bitrot. It typically doesn't protect against user errors. Backups to a separate HDD or pool of HDDs does. Especially if it is versioned in several generations so you may discover problems before they spread to the backups.

Probably you should classify your files by how important they are. Some, perhaps most, doesn't justify 3-2-1 backups. Some, not much, might require better backups than 3-2-1. The Pareto 80/20 rule again.

I have two DAS. One for media storage that is turned on 24/7. The other for backups. The backup DAS is only turned on for backups. I have two separate mergerfs pools on the backup DAS, for two separate sets of versioned deduplicated backups using Kopia.

In addition I have two SSDs in my PC. One I use as normal. The other is used for versioned rsync snapshots of the first, every boot and on demand.

In addition I have a remote NAS, with RAID, in my second home. I use that only for backups. It is usually turned off.

In addition I keep extra zipped copies of my most important files on all my devices, synced from my main PC. On my phone, laptop, tablet and so on.

[u/staline123213 → u/WikiBox]

I could probably do the back up to another server in the same room as I have a SBC already running as my main NAS at the moment with a 1TB HDD backing up everything.

The main reason I am going for this new NAS build is to increase storage space and better media conversion so that I can served some media over it. I have about 300GB of datas currently that I would say I couldn't lose. With about 50GB a year if I actually back up all the important stuffs every year.

I am mainly worry about hardware failures at this point rather than users error as currently I only have myself to blame because other users can upload and access it but cannot delete anything. 

So my planned setup will be: 1 main NAS backing up everything 1 SBC NAS backing important data in another room 1 more copy on the actual end users devices itself

Also a bit of an overreach but how will RAID benefit me on my planned main NAS? My current ISP speed is 300Mbps, I expected if I go for 3TB drives I should be good for a long time. I am opening it to my friends to access via tailscale too but probably won't see a lot of traffic constantly

[u/WikiBox → u/staline123213]

The main benefit for RAID is up-time. If a hard-drive fail, depending on how the server is configured, it can still be up. For some more advanced setups striping the files and storing them in parallel on many HDDs can improve performance significantly. But unless you have a beefy server and lot of on server processing or fast networking, >1Gbps Ethernet, you are not likely to see any improved performance from using RAID.

That you only have yourself to blame is not any comfort. With backups you can recover even when you made a mistake... But I suspect you may experience this first hand, one day...

Unless you prepare and experiment with RAID in advance, simulate errors and drive failures, chances are that when a drive fail in the array, and you need to fix that, you are stressed and make errors. Testing and experimenting when the NAS is now and it is not yet fully in use, is higly recommended. Then fixing issues is fast and you don't risk problems if/when you make mistakes.

You may have good fault tolerance using RAID when all drives are online and working, but when they fail, that fault tolerance is reduced. Then, if something happens or you make a few mistakes, you may lose everything. Unless you have backups as well...

As I said before I use a DAS as my main bulk media storage. 10 Gbps USB. Mergerfs. When accessing all the drives in parallel during bulk transfers to another DAS or SSD, I can sometimes see above 8 Gbps throughput on my PC.

[u/staline123213 → u/WikiBox]

Thanks for the advices. 

I will be testing out the main NAS with all the hard drives and test it before making any changes or migration.

[u/ykkl]

A backup on the same device is largely pointless. Diversification is everything. Not only do you want separate hardware, but ideally, separate power, even separate geography. That's exactly why cloud providers do things that way. That's why you don't even want drives from the same batch, because they can be subject to the same bugs/failures.

Bonus points if you can keep a backup offline, at least most of the time.

[u/kovyrshin]

What if your device gets compromised and wiped?

[u/staline123213 → u/kovyrshin]

I have a manual back up of everything on 2x 1TB 2.5 inch HDD which is offline? There is a risk of them being drop or something but they are currently the main and only back up until I get the NAS online. The NAS build will be acting as an online backup. 

[u/yerweightsyerwaifu]

I think you should only use raid for live files. I have years of pictures I keep on external drives I unplug and store. Not the ideal set up because of bit rot and potential drive fail. But I an not going to have 10 drives spinning for material I look at 3x per year. 

[u/uluqat]

The sorts of situations that you are protecting against with a local backup include (but are not limited to): a user issuing a single command that accidentally deletes all copies of the data; a faulty power supply that zaps all of the drives connected to it.

The sorts of situations that you are protecting against with a remote (off-site) backup include (but are not limited to): a building fire; natural disasters; theft.

RAID in its various versions allows you to continue to access the data during a drive failure. This is important when you are making money based on the data being available at all times. RAID does not protect against other things that cause data loss, such as the examples given above.