Hi all,
On 10/11/06, Bill Hacker <[EMAIL PROTECTED]> wrote:
Jamie wrote:
(...)
> > About ~ 1 mb/sec across a 100mbs ethernet connection. Correct me if I'm > wrong, but shouldn't this be closer to 5-10 megabytes/sec, assuming 100mbs > is "bits pr. second" and NFS had a rather large overhead? (say, 1/2 of it > is protocol related?) With the most-bandwidth-efficient of uncompressed protocols (never mind 'robust' for the moment) such as IBM bisync or RS-232 serial, you can treat a 'byte' as 10 bits, rule of thumb. It goes downhill from there - ethernet itself being *much* less b/w efficient than, for example, ARCnet/TCNS or even 100VG-Any-LAN, and TCP/IP less efficient on low-latency transmission paths than, for example SNA or even IPX/SPX. File-system overhead aside, 40% overhead is probably close for most TCP/IP over ethernet applications, so, yes - 50% overhead should be close.
humm, How come I can get 11 MB/sec copying a big divx file, through a ssh connection, ethernet LAN with 2 hops, cypher: blowfish? Thats: SSH + TCP + IP, copying a divx file, which isn't much reduced with ssh compression enabled... That doesn't fit right with the 40% overhead just for TCP/IP. Also, by checking out ethernet frame structure and TCP/IP packet structure.. its possible to have quite a low overhead... IP packet max size: 65K IP packet header size: 160bits TCP packet header size: 160bits. so for TCP/IP, we can have: 320bits of headers and 1500x8 bits of data. (so we avoid fragmentation of the IP packet when we stuff it in a ethernet frame...) that's not that much overhead. for ethernet: header: 14bytes data: 1500bytes crc: 4bytes again.. not that much overhead. It's just a question of packing those (ethernet) frames full of big IP/tcp packets... so, summing up: ethernet + tcp/ip: 144+320 bits of headers and: 11 680 bits of data. ( 11680/1518*8 ~ 0.96 ...) thats: ~ 0.96 of ideal bandwith efficiency. Or .. best possible overhead: ~4% Basically, if the OS knows its going to stuff IP packets in a ethernet frame, he should make them with the size of the ethernet MTU... (assuming a max MTU = ethernet frame) Also, AFAIK nfs is one of the most bandwith eficient network FS, with good speeds for a low number of clients... Although I assume I have not benchmarked NFS performance myself. the ooint being: nfs doesn't have a rather large overhead...
(...) HTH, Bill
Best regards -- Miguel Sousa Filipe
