Rob wrote:
Hello,
I have a cluster, master + 8 nodes, connected via
a Netgear Gigabit Ethernet Switch (model JGS516).
The cables are of CAT5 type.
Elsewhere I read that for a gigabit network, one
should use CAT6 type cables, to avoid bad
transmissions. Is that so?
Well, there is some debate about this. First, note that
nominally CAT5 is rated for gigabit speeds. Second, note
that gigabit cable does not really carry gigabit rate
transistions, but "only" 250MHz. However, ISTM that
even that is a bit much for simple twisted pair, even if
it is impedance controlled.
I already have done basic speed checks, that indicate
a throughput of about 0.5 Gbps. Hence the network
appears to operate on half of its spec. speed.
That appears quite good to me. 50% occupancy is not
bad.
Question 1:
Should I worry about this reduced speed?
No, I don't think so. What have you got filling the pipe?
Also, what protocols are you using? If you have to wait
for an ACK from time to time, then you are going to get
less than full BW. Also, protocols have other overhead,
like headers on messages and CRCs and whatnot.
Question 2:
How to check the transmission quality?
Should I inspect the output of "/sbin/ifconfig eth0"
for errors/dropped/overruns/collisions etc. in the
RX/TX lines?
Yep.
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:76:DF:1B:0D
inet addr:172.17.205.79 Bcast:172.17.255.255 Mask:255.255.0.0
inet6 addr: fe80::20c:76ff:fedf:1b0d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1924127 errors:0 dropped:0 overruns:0 frame:0
TX packets:1368176 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2416670249 (2304.7 Mb) TX bytes:99499187 (94.8 Mb)
Interrupt:11 Base address:0xc800
# uptime
23:00:36 up 7 days, 12:38, 11 users, load average: 0.20, 0.17, 0.17
Admittedly, just me on my machine, so limited data. But it seems
that I never miss a packet.
Mike
--
p="p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
This message made from 100% recycled bits.
You have found the bank of Larn.
I can explain it for you, but I can't understand it for you.
I speak only for myself, and I am unanimous in that!
