The short explanation is you have at minimum three drives, and you "stripe and span" them. This is a setup called RAID 5 where, if any one of the three drives fails, it can be replaced with a similar-sized drive and the "parity bits" from the other two drives can rebuild the data on the third drive. Yes, this means you only have the effective space of only two out of the three drives. So say you had 3x4TB drives, you'd have a total of 8TB to work with, and one drive is the "parity" drive (although this is actually split among the drives, so if any one fails, it can be revived by the other two).

However, in practice, the space lost is worth it for redundancy. It does mean an up-front cost in buying drives, a NAS enclosure (or using something like TrueNAS plus off the shelf parts to build your own), and includes the cost of physical maintenance and support (a Uninterruptible Power Supply to keep the hardware safe, for instance, on top of eventual maintenance of physical parts).

The offers the cloud solutions seem cheap up-front, but they don't buy you as much time as the one-time up-front cost of building your own NAS and maintaining it. I understand why people choose the cloud solutions, it's much easier. But if you're dedicated to this lifestyle, it's something worth looking into, at the very least.

[–] brygphilomena@lemmy.world 25 points 8 months ago (2 children)

Obligatory raid isn't backup.

While yes, this will protect you from a disk dieing if you monitor it enough to notice. But it doesn't save you from a nas dieing. Maybe you could rebuild the array with similar hardware but that's not a sure thing.

[–] CosmicTurtle@lemmy.world 14 points 8 months ago

This exactly. NAS+RAID gives you a backup of your local media. It can account for one of your three copies and one of your storage mediums. But you still need something off site.

So assuming you had a copy on your computer proper, it could work. Better than no backups.

[–] ArcaneSlime@lemmy.dbzer0.com 3 points 8 months ago

Not trying to be a dick just trying to help, but,

Dying*

[–] Solemn@lemmy.dbzer0.com 4 points 8 months ago

Backblaze personal is $9 a month or $99 a year for unlimited backup. The first result on Amazon for a 4tb HDD is $85. Building a NAS costs the same as 2.5 years of this cloud backup for the drives alone, and doesn't actually give you a backup at all. The costs scale even more poorly if you need to store more than your 8tb.

https://www.raidisnotabackup.com/

[–] ArtificialLink@lemy.lol 3 points 8 months ago

Serverbuilds.net. its really not that much up front cost.

[–] far_university1990@feddit.de 3 points 8 months ago

raid cannot repair corruption/bitrot. zfs/btrfs with redundancy can.