EsoErik

I tried storing an 8GiB virtual box disk image on BTRFS. Well, it copied over successfully, but minutes into 'pacman -Syu', the Linux instance in the VM began reporting copious IDE errors. Suspecting BTRFS copy-on-write being an issue, I moved the disk image back to a ZFS volume. This took inordinately long - it definitely was a COW issue. BTRFS went absolutely crazy as the VM wrote here, there and everywhere to its virtual disk, requiring a competent copy-on-write implementation - which BTRFS does not have.

That VM, again on ZFS, is again working flawlessly. ZFS is a copy-on-write filesystem and works. BTRFS is a copy-on-write filesystem and does not work.

We're how many years into BTRFS being officially "stable"? And it blows chunks the instant you attempt to, say, modify a file a lot? That doesn't seem right. Perhaps I'm the only one, and I'm doing something wrong? Nope. BTRFS just plain sucks.

The thing I did wrong with BTRFS was using BTRFS. Apparently, I could disable BTRFS's copy-on-write support for my VM disk image files. But, then my VM disk image files would have no FS-level data checksums or snapshot capability. If that's what I wanted, I'd keep my VM images on XFS or EXT4. It's not, and BTRFS is apparently little better than EXT4 with some additional features that don't work, so ZFS it is.