Roeland M.J. Meyer
rmeyer at mhsc.com
Tue Sep 30 10:12:14 GMT 1997
At 06:38 PM 9/30/97 +1000, Bond, Jeffery wrote:
>On my samba server, which is an ancient 486DX4 with only 8Mb, running
>FreeBSD, I usually see about 500KB/s when transferring large files over
>10Mbit ethernet. Only one or two clients are usually connected. I've no
>idea about NT, because I've never used it, but 500KB/s seems fast to me.
>What is the max 'raw' throughput of 10Mbit ethernet anyway? About
To calculate maximum theoretical through-put, do this; Note that this
procedure only produces a first order (back-of-the-napkin) approximation.
base = 10 Mhz = 10 Mbps (bits-per-sec)
FDX = base / 8 = Raw = 1.25 MBps (bytes-per-sec)
Note: the above is raw bytes per second (Bps), one-way. The only way you'll
actually see this is with an Full-Duplex(FDX) 10baseT switch. Ethernet is
normally Half-duplex(HDX) so the practical through-put is half of the Raw.
Allowing for normal operations (co-ax baseband.[10base2])
HDX = Raw / 2 = NetSpeed = 625KBps
This is completely ignoring protocol over-head as well as other traffic on
the wire. Your 500 KBps indicates;
HDXoverhead = (625K - 500K) / 625K = 20%
FDXnet = 1.0MBps
HDXnet = 500KBps
This is actually quite good, real close to theoretical maximums. The other
fellow, talking about 800KBps, must have been talking about a 100baseTX LAN
with other traffic slowing things down, or they had a FDX switch, rather
than a HUB/router. Still they had to have other traffic. Basic ethernet
just can't go that fast.
A long time ago, when I was doing OSI protocols for Retix, we were
seriously worried about this through-put, on IBM XT's, being more than the
processor could handle. We actually slowed the stack down to avoid packet
retries. The practical limit, for an IBM XT, was 600KBps, bus through-put,
with 8088 at 4.77 Mhz clock-rate. If we had an ST-506 disk access, at the
same time, we were definitely going to miss packets, no matter what we did.
This was around 1983-4.
However, with 100baseTX, this is a little faster;
base = 100 Mhz
FDX = 12.5 MBps
HDX = 6.25 MBps
Assuming 20% overhead
FDXnet = 10MBps
HDXnet = 5 MBps
Compared with a T1, assuming the same 20% overhead;
Note that FDX figures for T1's are irrelevent.
base = 1.54 Mhz
HDX = 96.25KBps
HDXnet = 77KBps
Note: I have NFS between my two Linux servers. Someday, I'll do some
through-put comparison testing.
Morgan Hill Software Company, Inc.
Roeland M.J. Meyer (RM993)
e-mail: mailto:rmeyer at mhsc.com
Colorado Springs, CO - Livermore, CA - Morgan Hill, CA
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