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Gigabit switches - expected server to server speeds?

Craig Norborg
Level 4
Level 4

I have some of our server infrastructure people working on building a test environment for a new application we want deployed. In doing so they need to copy very large files (90Gigabytes) from server to server.

I set them up on their own VLAN. They have 3 servers, each connected to a 3750G-24TS or 3750G-48TS switch on our network. The core of our network is a Catalyst 6500/ Sup720 running Native IOS. The switches they're on are trunked to our 6500's.

They are trying to copy these files from a server on one switch to a server on another one. They would go through the 6500 for this, but they are both on the same VLAN so the traffic isn't routed at all. When doing so the best they get is 100-120 Megabits/second.

However, if we take a 3750G-24TS and hook both servers directly into it and do the same copy, they get over 500 Megabits/sec throughput.

Each switch has a 1Gb uplink to the core. These uplinks are typically less then 2% utilized with bursts up to 5% utilization.

I might expect a little bit of a slowdown, but thats quite a bit more of a drop than expected...

Any ideas why the performance is so low? Any ideas where to look? I've looked at all the "show int <mod>/<port> counter errors" or "show controllers ethernet-controllers" I can and there is no indication of any error or anything??

7 Replies 7

a12288
Level 3
Level 3

I would like to know what throughput you could get if you just short-cut two servers via a cross over patch cord? 100-120 is way too slow.

bhedlund
Level 4
Level 4

What specific line card(s) are the 3750s connecting to on the 6500? Are they connected to the same line card or different?

We did have them on a couple of different linecards, but moved them to the same linecard (WS-X6516A-GBIC) and had about the same results, maybe a little bit better, but not significantly.

akemp
Level 5
Level 5

Interesting scenario indeed! What's the configuration of your uplink trunks look like ? Single vlan ? Static or VTP trunking ? What type of GBIC & fiber type or are your uplinks copper ?

802.11q trunk. Probably 5 vlans. VTP is turned off. GBIC would be SX, fiber type 62.5 micron multimode.

Danilo Dy
VIP Alumni
VIP Alumni

Be careful with this, when you tell your application people that your switch can provide this blah blah blah throughput, they will expect that throughput. Take note that to push that much data , server resources is one of the bottleneck. Also application is another bottleneck, depends on how it was build and the settings (throttling)

Just a word of advice, so you don't find yourself a fall guy during this test. Because you know, application people don't think :)

Pavel Bykov
Level 5
Level 5

We have the same configuration, but with 6748 linecard on 6506/720, and we get full throughput, limited only by header sizes.

from what you say it's not possible to pinpoint the problem.

- Have you tried connecting both servers to the 3750-48TS?

- Have you tried connecting both 3750's to another linecard? (e.g. different than 6516 but so the 3750's are still on the same linecard)

- Have you tried connecting 3750 end-to-end, without 6500 in the middle?

- Have you tried creating etherchannel as uplink?

- Have you looked at CPU/buffers on 6500?

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