Btrfs came default with my new Synology, where I have it in Synology's raid config (similar to raid 1 I think) and I haven't had any problems.

I don't recommend the btrfs drivers for windows 10. I had a drive using this and it would often become unreachable under load, but this is more a Windows problem than a problem with btrfs

What kind of disks, and how is your ZFS set up? Something seems amis here.

Raid 5/6, only bcachefs will solve it

Did you set the correct block size for your disk? Especially modern SSDs like to pretend they have 512B sectors for some compatibility reason, while the hardware can only do 4k sectors. Make sure to set ashift=12.

Proxmox also uses a very small volblocksize by default. This mostly applies to RAIDz, but try using a higher value like 64k. (Default on Proxmox is 8k or 16k on newer versions)

https://discourse.practicalzfs.com/t/psa-raidz2-proxmox-efficiency-performance/1694

Don't use btrfs if you need RAID 5 or 6.

The RAID56 feature provides striping and parity over several devices, same as the traditional RAID5/6. There are some implementation and design deficiencies that make it unreliable for some corner cases and the feature should not be used in production, only for evaluation or testing. The power failure safety for metadata with RAID56 is not 100%.

https://btrfs.readthedocs.io/en/latest/btrfs-man5.html#raid56-status-and-recommended-practices

You shouldn't have abysmal performance with ZFS. Something must be up.

I am using btrfs on raid1 for a few years now and no major issue.

It's a bit annoying that a system with a degraded raid doesn't boot up without manual intervention though.

Also, not sure why but I recently broke a system installation on btrfs by taking out the drive and accessing it (and writing to it) from another PC via an USB adapter. But I guess that is not a common scenario.

A bit of topic; am I the only one that pronounces it "butterface"?

No reason not to. Old reputations die hard, but it's been many many years since I've had an issue.

I like also that btrfs is a lot more flexible than ZFS which is pretty strict about the size and number of disks, whereas you can upgrade a btrfs array ad hoc.

I'll add to avoid RAID5/6 as that is still not considered safe, but you mentioned RAID1 which has no issues.

One day I had a power outage and I wasn't able to mount the btrfs system disk anymore. I could mount it in another Linux but I wasn't able to boot from it anymore. I was very pissed, lost a whole day of work

I've been using single-disk btrfs for my rootfs on every system for almost a decade. Great for snapshots while still being an in-tree driver. I also like being able to use subvolumes to treat / and /home (maybe others) similar to separate filesystems without actually being different partitions.

I had used it for my NAS array too, with btrfs raid1 (on top of luks), but migrated that over to ZFS a couple years ago because I wanted to get more usable storage space for the same money. btrfs raid5 is widely reported to be flawed and seemed to be in purgatory of never being fixed, so I moved to raidz1 instead.

One thing I miss is heterogenous arrays: with btrfs I can gradually upgrade my storage one disk at a time (without rewriting the filesystem) and it uses all of my space. For example, two 12TB drives, two 8TB drives, and one 4TB drive adds up to 44TB and raid1 cuts that in half to 22TB effective space. ZFS doesn't do that. Before I could migrate to ZFS I had to commit to buying a bunch of new drives (5x12TB not counting the backup array) so that every drive is the same size and I felt confident it would be enough space to last me a long time since growing it after the fact is a burden.

The question is how do you get a bad performance with ZFS?

I just tried to read a large file and it gave me uncached 280 MB/s from two mirrored HDDs.

The fourth run (obviously cached) gave me over 3.8 GB/s.