[abotsis]

It’s worth noting that much of the premise of the article (wanting flexibility) is outdated. Zfs has support for removing top-level raid 0/1 vdevs now. So you can take a raid10 pool, and remove a top level mirror vdev completely. Note that this doesn’t work for raid5/6 vdevs, but as the author points out, those are becoming less and less used because of rebuild time and performance.

In addition to the slew of other features Btrfs is missing (send/recv, dedup, etc) zfs allows you to dedicate something like an Intel optane (or other similar high write endurance, low latency ssd) to act as stable storage for sync writes, and a different device (typically mlc or tlc flash) to extend the read cache.

[kstrauser]

I think there's a selection bias here: people using RAID 5/6 may not be using ZFS as much because it's not well supported. I'd bet money that those levels are much more common in SOHO settings than RAID 10 is, because it's still the sweet spot for "I need lots of storage" vs "...and am willing to spend drive's worth of storage on availability". For instance, anyone using a NAS primarily as a backup target for desktops and small servers may love RAID 5, but be unwilling to throw money at a "better" RAID 10 setup.

[the8472]

btrfs has send/recv. And dedup, which is more efficient that ZFS' since it can be performed offline, on select parts of the filesystem and doesn't have to keep gigabytes of dedup tables in memory.

[herf]

zfs remove is not a very good implementation - it keeps the old blocks around (as a virtual device) and redirects them to new locations. This is fine for "oops I accidentally added a device" but not great otherwise.

[abotsis]

*Just kidding on send/recv, looks like it’s there now. Substitute with encryption if you need another example.