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Why is my ftp transfer between two 100Mb machines so slow on SCO Unix?

© Anthony Lawrence, aplawrence.com

Updated September 2009

Or any other slow ftp issue.

Usually this sort of thing is from bad (cheap) Nic cards and/or mis-negotiation with the switch or just lousy drivers. Ftp does a lot of work; junk affects it more than simple http, telnet or ssh connections. The amount of data transferred is larger; larger packets mean more chance of losses from window sizes, misnegotiation and so on.

It is just slow CONNECTING and not slow after that, it's probably DNS (see Telnet/FTP is very slow to connect).

If performance is bad during the actual transfer, it is a packet issue somewhere - look for losses and errors (netstat, llistat) and check negotiation, retransmission and so on.

At FTP slow xfer SCO OpenServer 5.06? it was noted that 3c905A and B cards had NWAY negotiation difficulties. That same post suggested using traceroute to make sure that packets aren't going half way around the world to get next door.

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