On Tue, Sep 12, 2017 at 10:01:07AM +0000, Duncan wrote: > BTW, I am most definitely /not/ a VM expert, and won't pretend to > understand the details or be able to explain further, but IIRC from what > I've read on-list, qcow2 isn't the best alternative for hosting VMs on > top of btrfs. Something about it being cow-based as well, which means cow > (qcow2)-on-cow(btrfs), which tends to lead to /extreme/ fragmentation, > leading to low performance. > > I don't know enough about it to know what the alternatives to qcow2 are, > but something that not itself cow when it's on cow-based btrfs, would > presumably be a better alternative. Just use raw -- btrfs already has every feature that qcow2 has, and does it better. This doesn't mean btrfs is the best choice for hosting VM files, just that raw-over-btrfs is strictly better than qcow2-over-btrfs. And like qcow2, with raw over btrfs you have the choice between a fully pre-written nocow file and a sparse file. For the latter, you want discard in the guest (not supported over ide and virtio, supported over scsi and virtio-scsi), and you get the full list of btrfs goodies like snapshots or dedup. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ I've read an article about how lively happy music boosts ⣾⠁⢰⠒⠀⣿⡁ productivity. You can read it, too, you just need the ⢿⡄⠘⠷⠚⠋⠀ right music while doing so. I recommend Skepticism ⠈⠳⣄⠀⠀⠀⠀ (funeral doom metal). -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
