Selfhosted

I use BTRFS w/ RAID 1 (mirror) with two drives (both 8TB), because that's all I've needed so far. If I had four, I'd probably do to separate RAID 1 pairs and combine them into a logical volume, instead of the typical RAID 10 setup where blocks are striped across mirrored sets.

RAID 5 makes sense if you really want the extra capacity and are willing to take on a little more risk of cascading failure when resilvering a new drive.

ZFS is also a great choice, I just went w/ BTRFS because it's natively supported by my OS (openSUSE Leap) with snapshots and rollbacks. I technically only need that for my root FS (SSD), but I figured I might as well use the same filesystem for the RAID array as well.

Here's what I'd do:

1. 4x 16TB HDDs either in a RAID 10 or two RAID 1 pairs in one logical volume - total space is 32TB
2. 500GB SSD -> boot drive and maybe disk cache
3. 8TB HDD - load w/ critical data and store at work as an off-site backup, and do this a few times/year; the 4x HDDs are for bulk, recoverable data

That said, RAID 5 is a great option as well, as long as you're comfortable with the (relatively unlikely) risk of losing the whole array. If you have decent backups, having an extra 16TB could be worth the risk.

https://forums.lawrencesystems.com/t/freenas-truenas-zfs-pools-raidz-raidz2-raidz3-capacity-integrity-and-performance/3569

RAID does not work today with any disks you may have: https://www.youtube.com/watch?v=l55GfAwa8RI

.The only sane option is ZFS with zRAID1/2.

Just remember if the data is important, raid is not backup. Have the media in another place. I have like 40-50 1tb drives I’ve copied stuff too in case everything goes belly up. Restoring won’t be fun but it will be possible.

If it were me personally, I’d get two more 16 tb drives and Raid 6 the whole thing. But that’s only because you’ve got the NAS already. If I just had the drives I’d set up a JBOD and either use TrieNAS, Unraid, or maybe OpenMediaVault.

I use raid5 on an HP server, and am dealing with 2 drive failures, because HP's qc is garbage. Raid6 would have saved me here, but it's not really likely to have 2 drives fail simultaneously, so... yeah.

I recommend looking into 321 backup, too. Raid isn't a backup solution, but it seems you already understand that and are trying to do that.

In the last 25 years working with approximately 700 servers that used RAID 5 I saw two of them lose an entire volume. Once was due to a malfunctioning HP RAID controller, and the other was due to a second disk dying while the rebuild from the first failure was still ongoing. There turned out to be a systemic problem with that drive model’s firmware which almost certainly contributed.

So in my experience it’s rare but it definitely does happen.

It can get worse. About 20 years ago the company I was at had an EMC tech yank the wrong power supply from a Symmetrix rack, where the other supply had earlier in the day caught fire! We lost that entire rack’s data (customer’s personal email accounts) due to data corruption. It was probably around 300 10k SCSI disks in that rack, a multimillion dollar expense at the time, and we had to restore all of it from tape over many, many days. Really, really sucked.

Odds are strongly against a 2 drive failure at your scale, though it does happen. I set my NAS up about 8 years ago, with 6 drives with raid-6 (well zfs's version) and in that time two drives have failed years apart. When you get two hundreds of drives total in your operation you will see a dual drive failure.

Though you still really should have backups of everything you care about. Even though odds are in your favor someone reading this will lose data in their life on their NAS system.

Use zfs, raid 10 the big drives, toss the 8tb, and use the ssd as a write cache.

Personally I use RAID5, with regular backups for documents and projects. Not too worried if my movies and tv library get lost…that takes up most of the space though.

Personally I'm more on the paranoid side, so I went with raid 6 and a hot spare. So in case of failure I can rebuild one disk immediately and not having to buy one first. But so far I've never had a disk failure.

In addition I was thinking of having the 8TB HDD as a standalone to backup the documents and maybe the photos and the docker setups.

That is a very good idea. I also can't quite afford to backup my main storage of movies/shows, but at least all the important personal documents (and my music) is properly backed up.

I'm fine with RAID5. Though I've seen the case where one drive failed and another one had several bad sectors and maybe was at the brink of failure, too. We were able to rebuild the RAID and replace both drives succesively but lost a few files. I think chances are slim, though. And even with RAID6, chances are your house burns down or lightning hits the neighborhood or a thief breaks in and takes the entire server. Or you or someone deletes stuff. So it doesn't really replace a backup in any case. I'd say RAID5 is fine for home use. Take backups of your most important files.