I believe you&#x27;re misunderstanding the problems that occur on a cow filesystem.  In fact btrfs already has an overcommit disk buffer, and is already doing many ENOSPACE handling tricks.<p>Have a look;
<a href="https:&#x2F;&#x2F;btrfs.wiki.kernel.org&#x2F;index.php&#x2F;ENOSPC" rel="nofollow">https:&#x2F;&#x2F;btrfs.wiki.kernel.org&#x2F;index.php&#x2F;ENOSPC</a><p>Reading more for my own interest it seams ZFS uses ZIL to help convert random writes to sequential, which helps with fragmentation under low space.  I am curious if bcache, can operate similarly.  In addition, I should also point out that this is less of an issue on SSD, due to the nature of how random reads&#x2F;writes work there anyway (btrfs does a good job of being SSD aware).