Dropped records when FTP from mainframe to server

[MLK2348]

Every month, we FTP over 200 files from the mainframe to a Windows server and it can take from 8-12 hours. Many of the files are very large and have to be split for the FTP. We are able to compare record counts (expected and received) and a few of the files have incorrect record counts and must be re-FTP'd. It's usually less than 50 records per file and happens to a random 2-10 files.

We tried limiting the number of FTP stream from 5 to 3 but that had no effect.

Where would be the first places to research to identify the cause? Reftp is a time consuming process because of the numerous large files.

MK

[MrSpock]

Is using PKZIP/GZIP or something similar to greatly reduce the filesizes not an option?

[sergeyken]

Is it possible to verify the result of FTP for each particular file?
Either on the fly, just after every FTP command, or after the fact - by the FTP log analyzis?

It should show the files in error, to repeat this FTP, either manually, or automatically.
Even for thousands of FTP...