On Thu, Jan 2, 2020 at 2:31 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > On Thu, Jan 02, 2020 at 07:25:34PM +0000, Hefty, Sean wrote: > > > > > Is it possible to transfer a large file, say 25GB, between two computers using > > > > > RDMA UD, and have an exact copy of the original file on the receiving side? My > > > > > understanding is that the order of the messages is not guaranteed with UD. > > > > > But I thought that if I only use one QP I could ensure that the ordering of the > > > > > data will be predictable. > > > > > > > > It is not guaranteed to be in order. > > > > > > > > Why would you do this anyhow? The overhead to use RC is pretty small > > > > > > > So even if I am using only 1 QP, it is still not guaranteed to be in > > > order. Ok. Thanks. > > > > The spec doesn't guarantee ordering, though I doubt messages would > > ever be unordered in practice. You could transfer a sequence number > > as immediate data to allow the receiver to verify (and correct) > > packet ordering, and detect lost packets. > > They could always become lost though, due to a link BER or > something. And that is only on IB, not Ethernet. > > I don't think you can avoid needing retransmit on the sender... > My plan was to try to send large files between two computers. >From many transfers, I was intending to get an estimate of what types of losses we could reasonably expect. From my reading, I got the impression that with a point to point connection, the expected message loss with RDMA UD was quite low. Terry
