On Tue, 2010-03-02 at 12:33 -0500, John Stoffel wrote: > >>>>> "Trond" == Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> writes: > > Trond> On Tue, 2010-03-02 at 11:10 +0800, Wu Fengguang wrote: > >> Dave, > >> > >> Here is one more test on a big ext4 disk file: > >> > >> 16k 39.7 MB/s > >> 32k 54.3 MB/s > >> 64k 63.6 MB/s > >> 128k 72.6 MB/s > >> 256k 71.7 MB/s > >> rsize ==> 512k 71.7 MB/s > >> 1024k 72.2 MB/s > >> 2048k 71.0 MB/s > >> 4096k 73.0 MB/s > >> 8192k 74.3 MB/s > >> 16384k 74.5 MB/s > >> > >> It shows that >=128k client side readahead is enough for single disk > >> case :) As for RAID configurations, I guess big server side readahead > >> should be enough. > > Trond> There are lots of people who would like to use NFS on their > Trond> company WAN, where you typically have high bandwidths (up to > Trond> 10GigE), but often a high latency too (due to geographical > Trond> dispersion). My ping latency from here to a typical server in > Trond> NetApp's Bangalore office is ~ 312ms. I read your test results > Trond> with 10ms delays, but have you tested with higher than that? > > If you have that high a latency, the low level TCP protocol is going > to kill your performance before you get to the NFS level. You really > need to open up the TCP window size at that point. And it only gets > worse as the bandwidth goes up too. Yes. You need to open the TCP window in addition to reading ahead aggressively. > There's no good solution, because while you can get good throughput at > points, latency is going to suffer no matter what. It depends upon your workload. Sequential read and write should still be doable if you have aggressive readahead and open up for lots of parallel write RPCs. Cheers Trond -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
