On Sun, Dec 20, 2009 at 12:27 AM, Dan Nelson <dnel...@allantgroup.com> wrote: > In the last episode (Dec 19), Zaphod Beeblebrox said: >> Here's an interesting conundrum. I don't know what's different between >> the TCP that scp uses from the TCP that NFS uses, but given the same two >> FreeBSD machines, SCP fills the pipe with packets better. >> >> Examine the following graphic: http://www.eicat.ca/~dgilbert/example-mrtg.png >> >> The system doing the scp and the NFS server is FreeBSD-7.2-p1. The system >> receiving the scp and the NFS client is FreeBSD-8.0-p1 >> >> The scp transfer is the left hand side of the graph and the NFS transfer >> is on the right. >> >> The NFS is mounted with "-3 -T -b -l -i" and no other options. Files are >> being moved over NFS with the system "mv" command. The files in each case >> are large (50 to 500 meg files). > > If you increase the NFS blocksize (-r 32768 for example) you will get > slightly better performance, but you will likely never match the scp > results. They're doing two different things under the hood: scp is > streaming the entire file in one operation, while NFS is performing many > "read 8k at offset 0", "read 8k at offset 8k", etc requests one after > another, so a high-latency connection will take a performance hit due to the > latency in issuing each command. According to the mount_nfs manpage, it > looks like there is some prefetching that can be enabled with the "-a ##" > option. It doesn't say what the default is, though.
While the link is slow, it is really directly connected with a latency of 10ms or so. Isn't mv mmap()'ing large enough regions to cause there to be a reasonable queue to transfer? _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
