Recently we setup an isolated network for imaging HDD's. During this process we discovered that a 10Mb/sec hub had a better data transfer rate than a 10/100Mb/sec switch. This caused an old question to come screaming back to the forefront of my mind. I have heard, many times, that a 100Mb/sec ethernet network will only be able to achieve around 30Mb/sec throughput. I have not been able to find any information to validate this, but the aforementioned test seems to lend credit to this statement. Has anyone heard of or experieced this before?
The short answer to your question is "Yes", but the longer and more accurate response is that your question isn't specific enough.
1. Are you running switched Ethernet or shared Ethernet?
2. Are the network topologies the same between the hub and switch? (Are you going through more routers? Less routers? Different routers? More or less busy routers?)
3. Are you using the same access-level devices? Are they configured similarly?
4. Are you using half or full-duplex modes?
5. Are you using 10 Mbps or 100 Mbps?
6. Are there other devices on the same hub? On the same switch? Are all of the devices on the switch on the same VLAN?
7. Is spanning tree stable? Are you spanning? Is the switch using trunking?
To summarize: In general, switched media (a switch) will result in higher throughput/bandwidth then shared media (hub). Shared media systems (hubs) must deal with contention. If they don't, then they may approach the the throughput of switched media.
A properly configured switched network can easily surpass the 30 Mbps limit to which you refer which generally applies to shared Ethernet. The NT and Novell servers on the network I support easily approach (apparent) throughput rates in excess of 170+ Mbps (due to full-duplex mode). When they're misconfigured (of course, it's not a network problem - it's a server problem!), they drop to 10 Mbps or so....
Thanks for the reply! To answer the more detailed questions:
1. We are running this as a switched Ethernet network with the switch installed. With the hub is installed it functions as a shared Ethernet network.
2. The network topologies are identical, a server connceted to a hub/switch and one additional PC. We remove the hub and replace it with the switch. There are no other network devices (Routers, switches, hubs, etc.) on this network.
3. See answer 1 & 2.
4. The hub is running at half duplex and the switch is running full.
5. The hub is a 10Mb device, the switch was set to autonegotiate. It connected at 100Mb/full.
6. See answer 2.
7. The switch was set to default setting (out of the box).
I agree with your summary however, we experienced the complete oposite in this configuration. We even went as far as connecting the two machines (NIC to NIC) with a cross-over cable. The Hub configuration still out performed the other two configs.
I was curious as to what (hardware and/or software)are you using to measure your throughput?
Hm. You're only obtaining 30 Mbps through a switched Ethernet connection? That leads me to think there's a problem with the switch configuration.
The first which leaps out at me is spanning tree. Have you used the "set port host" command?
While Cisco has changed their official position, we tend to find that fixing or "nailing" duplex and speed settings to be helpful. You might want to try that.
What are your error rates on the switch ports? If you're showing high rates of errors, you might have a problem with the NIC's being used and their compatibility with the switch. Cisco has a list of known NIC's with problems on the LAN switching site.
As for measuring throughput, the question is what I don't have... I've got RMON probes, Sniffers, CWorks, Netview, homegrown stuff, other polling tools....
The only thing I would say is a DUPLEX mismatch. Auto negotiate is evil! Some NIC's will just set themselves to half while the other end uses full. Allways, with any switch, use a fixed setting on BOTH ends. When transferring big files, like the diskimages your trying to, DO use full duplex, but do not be surprised that you will find you do not see anything higher than 50Mbs. This is due to DISK speed of your server/workstation. Try copying the file up and down.
Also when using the cross-over cable make sure you set both machines fixed to full duplex.
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