I am using both. I've lost data on both, and near misses that required hair-raising metadata rebuild. BTRFS documentation still greatly trail behind ZFS, imo. It's RAID1 implementation is subpar in terms of monitoring.
> I've lost data on both Can I ask about the circumstances of losing data on ZFS? I've been viewing it as 100% rock-solid, so I'd very much like to know about any failure modes I'm missing.
iscsi target image file on ZFS RAIDZ zpool. I don't think it had much to do with iscsi though- the image file was affected because it's a TB-size file with lots of read/write. IIRC there were 2 other files that were also corrupted, but their sizes were in the range of teen GBs. I haven't seen any corruption from that installation since then.
The corruptions were identified by scrub after an unexpected restart, but the files were already corrupted before that (the system that was using the iscsi target behaved strangely whenever it accessed the drive.)
Server: Lenovo 3U server Xeon E5 v2 with ECC ram. I forgot what's the controller.