In my experience btrfs is not suitable for anything.

Unfortunately, I've learned this the hard way. Twice.

I'm sure it's more stable now than it was when I used it last, but it's frustrating when people say "no, this time it's really stable!" and then you lose data due to a bug. This same thing has never happened to me with ZFS on Linux, which is a shame because the licensing issues make it painful for me to use. I like up to date kernels.

I feel like btrfs should be phased out. It was clearly developed in a fashion that did nothing to prevent preventable bugs. This may be the same frustration that's leading RedHat to work on their own competing filesystem...

Any suggestions for a dynamically grow-able/shrinkable system of mixed drives for linux? When I last looked (and why I went with Storage Spaces) was that ZFS requires pools to be fixed at initialization, and I wasn't sure what other OSS solutions were mature at the time.

I have no suggestions honestly, I have looked into it pretty extensively and would like to go ZFS. But it will cost a decent amount for the setup I am looking for. It seems to be "all or nothing"