On Mon, Oct 1, 2012 at 9:47 AM, Tommi Virtanen <[email protected]> wrote: > On Thu, Sep 27, 2012 at 11:04 AM, Gregory Farnum <[email protected]> wrote: >> However, my suspicion is that you're limited by metadata throughput >> here. How large are your files? There might be some MDS or client >> tunables we can adjust, but rsync's workload is a known weak spot for >> CephFS. > > I feel like people are missing this part of Greg's message. Everyone > is so busy benchmarking RADOS small I/O, but what if it's currently > bottlenecked by all the file-level access operations that interact > with the MDS? Rsync causes a ton of those.
Yes. Bryan, you mentioned that you didn't see a lot of resource usage — was it perhaps flatlined at (100 * 1 / num_cpus)? The MDS is multi-threaded in theory, but in practice it has the equivalent of a Big Kernel Lock so it's not going to get much past one cpu core of time... The rados bench results do indicate some pretty bad small-file write performance as well though, so I guess it's possible your testing is running long enough that the page cache isn't absorbing that hit. Did performance start out higher or has it been flat? > If you want to benchmark just the small IO, you can't compare rsync to rsync. > > If you want to benchmark just the metadata part, rsync with 0-size > files might actually be an interesting workload. -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
