On Fri, Jun 10, 2011 at 12:48:36AM +0200, Johannes Hirte wrote: > I've observed several times that after a btrfs filesystem defrag a file was > way > more fragmented than before. For example, a file that was recently written, > had > 10 extents (output from filefrag). After a defrag filefrag showed more than > 1900 > extents. > For curiosity, a simple copy of this "defragmented" file reduced the > number of fragments to 1. With a different file I got 63 extents before and > over > 3000 extents after defrag.
Do you have compression enabled? Or autodefrag mount option? 'filefrag -v' will tell you size of the extents, would be interesting to see. > It's no problem if defrag can't reduce the fragmentation. But in this case it > shouldn't be done at all. AFAIK defragmentation just reads the file, marks all pages dirty and lets it be written back. If the free space is fragmented, so will be the newly written copy. I do not know if there is some logic comparing old and new extent layout (or if it's even possible). david -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
