They most likely run smaller pools and have their redundancy and replication provided by the application layers on top, replicating everything globally. The larger you go in scale, the further up in the stack you can move your redundancy and the less you need to care about resilience at the lower levels of abstraction.

ZFS is fairly slow on SSDs and BTRFS will probably beat it in a drag race. But ZFS won’t loose your data. Basically, if you want between a handful TB and a few PB stored with high reliability on a single system, along with ”modest” performance requirements, ZFS is king.

As for the defaults - BTRFS isn’t licence encumbered like ZFS, so BTRFS can be more easily integrated. Additionally, ZFS performs best when it can use a fairly large hunk of RAM for caching - not ideal for most people. One GB RAM per TB usable disk is the usual recommendation here, but less usually works fine. It also doesn’t use the ”normal” page cache, so the cache doesn’t behave in a manner people are used to.

ZFS is a filesystem for when you actually care about your data, not something you use as a boot drive, so something else makes sense as a default. Most ZFS deployments I’ve seen just boot from any old ext4 drive. As I said, BTRFS plays in the same league as Ext4 and XFS - boot drives and small deployments. ZFS meanwhile will happily swallow a few enclosures of SAS-drives into a single filesystem and never loose a bit.

tl;dr If you want reasonable data resilience and want raid 1 - BTRFS should work fine. You get some checksumming and modern things. As soon as you go above two drives and want to run raid5/6 you really want to use ZFS.

Look, there is a reason everyone who actually knows this stuff use ZFS. A good reason. ZFS is really fucking good and BTRFS has absolutely nothing on it. It’s a toy in comparison. ZFS is the gold standard in this class.

You have four sane options:

• mdraid raid5 with BTRFS on top. Raid5 on BTRFS still isn’t stable as far as I know, not even in 2026.
• Mirror or triple mirror with mdraid. Have the third drive in the pool as more redundancy or outside the pool as separate unraided filesystem.
• Same as above, but BTRFS. Raid1 is stable.
• ZFS RaidZ1 (=raid5)

(Not sure about bit rot recovery when running BTRFS on mdraid. All variants should at least have bit rot detection.)

To reiterate, every storage professional I know has a ZFS-pool at home (and probably everywhere else they can have it, including production pools). They group BTRFS with Ext3, if they even know about it. When I built my home server, the distro and hardware was selected around running ZFS. Distros without good support for ZFS were disregarded right away.

I started experimenting with the spice the past week. Went ahead and tried to vibe code a small toy project in C++. It’s weird. I’ve got some experience teaching programming, this is exactly like teaching beginners - except that the syntax is almost flawless and it writes fast. The reasoning and design capabilities on the other hand - ”like a child” is actually an apt description.

I don’t really know what to think yet. The ability to automate refactoring across a project in a more ”free” way than an IDE is kinda nice. While I enjoy programming, data structures and algorithms, I kinda get bored at the ”write code”-part, so really spicy autocomplete is getting me far more progress than usual for my hobby projects so far.

On the other hand, holy spaghetti monster, the code you get if you let it run free. All the people prompting based on what feature they want the thing to add will create absolutely horrible piles of garbage. On the other hand, if I prompt with a decent specification of the code I want, I get code somewhat close to what I want, and given an iteration or two I’m usually fairly happy. I think I can get used to the spicy autocomplete.