On Sun, Dec 7, 2014 at 1:32 PM, <ashf...@whisperpc.com> wrote: > > I disagree. My experiences with other file-systems, including ZFS, show > that the most common solution is to just deliver to the user the actual > amount of unused disk space. Anything else changes this known value into > a guess or prediction.
What is the "actual amount of unused disk space" in a 2x 8GB drives mirror? Very literally, it's 16GB. It's a convenience subtracting the space used for replication (the n mirror copies, or parity). This is in fact how df reported Btrfs volumes with kernel 3.16 and older. A ZFS mirror vdev doesn't work this way, it reports available space as 8GB. The level of replication and number of devices is a function of the vdev, and is fixed. It can't be changed. With Btrfs there isn't a zpool vs vdev type of distinction, and replication level isn't a function of volume but rather that of chunks. At some future point there will be a way to supply a hint (per subvolume, maybe per directory or per file) for the allocator to put the file in a particular chunk which has a particular level of replication and number of devices. And that means "available space" isn't knowable. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
