Hi, I am trying to parallely copy a range of files (using SMB) between two pairs of computers all connected over the same network. Let's call the computers A, B, C and D; I want to copy files from A to B and C to D at the same time.

These 4 computers are all connected to the same switch (a TP-Link TL-SG1016DT) which advertises 16 ports with 1000 Mbps each. So I would presume that A->B and C->D each will have a theoretical bandwidth of 1000 Mbps each (2000 total).

My test, I first confirm my assumption that A->B and C->D each have 1000 Mbps bandwidth. Each transfer is done using two files (80MB each).

    A->B : ~1.5 seconds
    C->D : ~1.3 seconds

160 / 1.5  = 106 MBps ~ 1000 Mbps (ok).

But when I start A->B and C->D at the same time

    A->B || C->D : ~2.8 seconds

320 / 2.8 = 114 MBps (not ok)

Which sort of suggests to me that the operation which I thought would be parallel isn't parallel at all. (I have checked my code and confirmed that the copy operation is in fact called roughly at the same time). Also someone suggested that I use ports 1,5,9,13 which made no difference.

Am I doing something wrong here?

Cheers.