ещё рекомендую space_cache=v2
> This space_cache option will be selected while mounting a mount point which has Btrfs file system. This will store the free space cache on the disk to make the caching of a block much faster. Without this, Btrfs has to scan the entire tree every time looking for the free space that can be allocated.
Options to control the free space cache. The free space cache greatly improves performance when reading block group free space into memory. However, managing the space cache consumes some resources, including a small amount of disk space.
There are two implementations of the free space cache. The original one, referred to as v1, is the safe default. The v1 space cache can be disabled at mount time with nospace_cache without clearing.
Once enabled, the v2 space cache will always be used and cannot be disabled unless it is cleared.