Excerpts from Erik Logtenberg's message of 2010-12-15 11:06:03 -0500: > 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] <file>|<dir> [<file>|<dir>...] > > 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: -v is verbose. It just prints the file name as it defrags -c forces compression, even if you are mounted without compression on -s is the starting byte you want to defrag in the file. This is useful for very large files that are only compressed in a particular spot -l is the number of bytes you want to compress, would be paired with -s -t is a threshold. If the extent is bigger than this threshold, we consider it defragged already. -f starts the IO right away. > > > filesystem defragment <file>|<dir> [<file>|<dir>...] > > 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. This is still true. > > I hope someone can shed some light on these subjects. > Hope this makes sense ;) -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
