On 02/12/2018 03:45 PM, Ellis H. Wilson III wrote: > On 02/11/2018 01:03 PM, Hans van Kranenburg wrote: >>> 3. I need to look at the code to understand the interplay between >>> qgroups, snapshots, and foreground I/O performance as there isn't >>> existing architecture documentation to point me to that covers this >> >> Well, the excellent write-up of Qu this morning shows some explanation >> from the design point of view. > > Sorry, I may have missed this email. Or perhaps you are referring to a > wiki or blog post of some kind I'm not following actively? Either way, > if you can forward me the link, I'd greatly appreciate it.
You are in the To: of it: https://www.spinics.net/lists/linux-btrfs/msg74737.html >> nocow only keeps the cows on a distance as long as you don't start >> snapshotting (or cp --reflink) those files... If you take a snapshot, >> then you force btrfs to keep the data around that is referenced by the >> snapshot. So, that means that every next write will be cowed once again, >> moo, so small writes will be redirected to a new location, causing >> fragmentation again. The second and third write can go in the same (new) >> location of the first new write, but as soon as you snapshot again, this >> happens again. > > Ah, very interesting. Thank you for clarifying! -- Hans van Kranenburg -- 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