I haven&#x27;t heard this and I&#x27;ve been on the btrfs list for years. The biggest issue you&#x27;re going to have at 80+% usage, that applies to all file systems getting slow, is transfer rate drops due to inner tracks having fewer sectors; and depending on the workload, seeks are increasing simply because there&#x27;s more stuff on the disk to go looking for.<p>As for fragmentation there are two kinds: fragmentation of files into more than one extent, fixed with &#x27;btrfs filesystem defrag&#x27; and also autodefrag. And the other is fragmentation of free space, as a result of deleting files and that&#x27;s fixed with &#x27;btrfs balance&#x27; which consolidates extents and writes them into new chunks then frees up large regions of contiguous space on the drives. This is best used with filters.