Austin S. Hemmelgarn posted on Mon, 21 Dec 2015 08:36:02 -0500 as excerpted:
> On 2015-12-16 21:09, Christoph Anton Mitterer wrote: >> On Tue, 2015-12-15 at 11:00 -0500, Austin S. Hemmelgarn wrote: >>> nodatacow only [avoids fragmentation] if the file is >>> pre-allocated, if it isn't, then it still ends up fragmented. >> Hmm is that "it may end up fragmented" or a "it will definitely? Cause >> I'd have hoped, that if nothing else had been written in the meantime, >> btrfs would perhaps try to write next to the already allocated blocks. > If there are multiple files being written, then there is a relatively > high probability that they will end up fragmented if they are more than > about 64k and aren't pre-allocated. Does the 30-second-by-default commit window (and similarly 30-second- default dirty-flush-time at the VFS level) modify this at all? It has been my assumption that same-file writes accumulated during this time should merge, increasing efficiency and decreasing fragmentation (both with and without nocow), tho of course further writes outside this 30- second window will likely trigger it, if other files have been written in parallel or in the mean time. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- 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
