IMHO bcachefs has important advantages over ZFS. It is far more flexible. ZFS is really similar to traditional block-based RAID. You can get pretty flexible configurations but 1. They are largely fixed after creation and 2. They only operate at "dataset" level granularity.
bachefs has a really flexible design here where you basically add all of your disks to the storage pool and then you can pick redundancy and performance settings per folder (arbitrary subtrees, not just datasets decided at setup time) or even file. For example you can configure a default of 2 replicas for all data, but for your cache directory set it to 1 replica. If you have an important documents folder you can set that to 3 replicas, or 4.2 erasure coding.
Similarly you can tell it to put your cache folder on devices labeled "ssd" but your documents folder should write to "ssd" but then be migrated to "hdd" when they are cold.
And again, all of this can be set at any time on any subtree. Not just when you initially set up your disks or create the directories.
bachefs has a really flexible design here where you basically add all of your disks to the storage pool and then you can pick redundancy and performance settings per folder (arbitrary subtrees, not just datasets decided at setup time) or even file. For example you can configure a default of 2 replicas for all data, but for your cache directory set it to 1 replica. If you have an important documents folder you can set that to 3 replicas, or 4.2 erasure coding.
Similarly you can tell it to put your cache folder on devices labeled "ssd" but your documents folder should write to "ssd" but then be migrated to "hdd" when they are cold.
And again, all of this can be set at any time on any subtree. Not just when you initially set up your disks or create the directories.