Traffic routing question

[UbuntuBantu]

This is probably a dumb question, but I've not been able to find the answer.

Scenario: you have three networked devices (A, B & C) all in the same subnet and connected via a switch. You want to copy data from device A to device C. Source and destination folders are shared via NFS and visible to all devices. Device B has a file manager installed.

Question: if you used the file manager on device B to do the copying, does the traffic get routed A->B->C or A->C?

[hlrguy]

Short answer is no. It doesn't matter whether same subnet or around the world. Using the file manager, you tell A to copy to C. A will use whatever default route or specific route (if you have one set up) to copy the file to C. The only time "B" would come into play is if it is some kind of proxy or involved in the route A would use to get to C, which isn't the case, A has a direct path to C.

hlrguy

[furrycat]

To understand the answer you have to think about what happens behind the scenes when you drag the file from one place to another in your file manager.

First the file manager will read a block of data from the source directory and write it out to a new file in the target. Then it will read the next block and write it out. The process repeats until the whole file has been copied.

So in other words, yes, the data is pulled over the network from A into memory on B then pushed to C to be written out to disk. It's the file manager which is doing the reading and writing and on each occasion it must access the network.

You can see the effect by copying from the file manager as described and also mounting A from C and doing a copy from there. It should be twice as quick. If you do the test from C immediately after the test from B you might find it's even quicker as A will have the file in cache and won't need to read it file from disk before being able to send it to B.

Not a dumb question by any means.

[hlrguy]

It must depend on the file manager since I have manged remote files over dialup, copying from place to place and can guaranteed it didn't transfer in/out of my dialup connection. I have used Konqueror with FISH, FTP and midnight commander, although MC night have been direct on "A". I will try NFS on Tuesday with Konqueror and test.

hlrguy