From mboxrd@z Thu Jan 1 00:00:00 1970 From: Erik Logtenberg Subject: What do the arguments of btrfs filesystem defragment do? Date: Wed, 15 Dec 2010 17:06:03 +0100 Message-ID: <4D08E76B.40400@logtenberg.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 To: linux-btrfs@vger.kernel.org Return-path: List-ID: Hi, I would like to know that the arguments of "btrfs filesystem defragment" do. According to the built-in help page, the invocation is as follows: > btrfs filesystem defragment [-vcf] [-s start] [-l len] [-t > size] | [|...] > Defragment a file or a directory. Unfortunately I can't find any documentation on the meaning of these arguments. The man page doesn't list these arguments: > filesystem defragment | [|...] > Defragment files and/or directories. Also the online documentation [1] is identical to the man page. [1] https://btrfs.wiki.kernel.org/index.php/Btrfs(command) On a somewhat related note I did find another page on the wiki [2] that explains a bit on the defragmenting subject, more specifically it mentions this rather important caveat: > Caveat: Defragmenting a file which has a COW copy (either a snapshot > copy or one made with bcp or cp --reflinks) will produce two unrelated > files. If you defragment a subvolume that has a snapshot, you will > roughly double the disk usage, as the snapshot files are no longer COW > images of the originals. [2] https://btrfs.wiki.kernel.org/index.php/Problem_FAQ >>From what I've heard on IRC this is still the case in current versions, but the Btrfs(command) documentation contains no mention of this. I hope someone can shed some light on these subjects. Kind regards, Erik.