ftp transfer rate varying very widely

[Gilbert Standen_1]

this morning we ftp'd some files from an hp unix box to a unix box and had fantastic transfer rates (120 Mb/min). Then we began offloading some of the files from the target box to another machine on that network. suddenly the ftp rate went almost to a crawl, and now, even though the offloading of the files on the target network long since completed, the rate is remaining very low. How can we regain those high rates ? Is it caused by network issues on the pipe from Michigan to NYC or is it something at the target server do you think ?

[RAC_1]

Check following things on target box and on onther machine.

NIC speed settings -- on NICs and on switch/routers.

If they differ, you are almost certain that this is the problem. Set those hard coded. If it is 100HD, set it 100HD, auto-off on NICs and on switch.

Anil

[rick jones]

Well, the rest of us know little to nothing about "the pipe from Michigan to NYC" so it would be hard for us to tell :)

There could be many reasons. I'm guessing the target box is not HP-UX or you'd have said that but still...

*) Yes, there may be a duplex issue. However, I'd not hardcode things until after you have confirmed there is a duplex issue. In HP-UX, you'd use lanadmin to check the duplex setting. Then, if it is half-duplex, a duplex mismatch will have _late_ collisions (other collisions don't "count" for this). If it is full-duplex, a duplex mismatch will have FCS (CRC) errors.

If you see that, keep in mind that both ends of the wire much have matching settings - either both auto, both full, or both half. You cannot have auto on one end and fixed at the other - auto (is supposed to) fail in that case and go to half at its end.

You also want to check TCP statistics - look for retransmissions - in particular the percentage. The beforeafter tool from ftp://ftp.cup.hp.com/dist/networking/tools/ can be used to subtract one set of netstat -s from another to make that easier - look while your slow FTP transfer is taking place. (Beforeafter will also work with lanadmin output and may work for other link-level stats output)

You might also run netperf TCP_STREAM tests - in particular, try altering the socket buffer sizes (-s and -S) and see how large a window maximizes the performance. perhaps the FTP sessions are not using a sufficiently large TCP window in one direction. www.netperf.org

[Ted Buis]

Try some pings to see how the network is responding. If ping performance is bad, then it is clearly a network only problem.