On Tue, 21 Apr 2009, Nicholas Lee wrote:
(*) 1Gbps is 125kB/ms and divide by two in order to account for switch - 62.5kB/ms. This means a maximum of 32MB/s bandwidth in a switched network for sync NFS IO. Have I missed something?
One obvious wrong assumption is the assumption that the switch is a "store and forward" device. Modern ethernet switches only consume enough data to validate the ethernet packet header before they start sending data on to the destination. This results in delays in the low microseconds. Unless the outbound switch port is overloaded, you should ignore the switch entirely. Normal switched ethernet is full-duplex. There is no need to divide by two for the switch.
Modern NFS uses TCP so the Naggle algorithm could become significant if the writes are very small (not applicable for your large packet).
I have measured NFS write rates of about 90MB/second using 32KB blocks and using a lowly 4-year old SPARC workstation with Solaris 10 as a client. The individual block writes might not have been synchronous though since NFSv4 supports a 'commit' feature.
Bob -- Bob Friesenhahn [email protected], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ storage-discuss mailing list [email protected] http://mail.opensolaris.org/mailman/listinfo/storage-discuss
