This is a limitation of how most FTP servers work and how PHP works.
Problem 1: Blocked by FTP server. In order to avoid server timeouts, the site transfer (essentially: a backup) has to be performed in multiple small steps. On each step we have to connect to the remote FTP server, log in, transfer a few files, log out. This roughly means that we have to do this log in, transfer, log out routine 3-4 times per minute over several minutes (or hours). This tends to cause most FTP servers to consider this behaviour as an attack and block logins from this IP for a while. The next time we try to connect to the FTP server we are blocked and the site transfer fails.
Problem 2: Large files. The definition of "large" mostly depends on the transfer speed between your original and your target servers. If a file takes too long to transfer it is possible that the FTP server closes its connection. It is also possible that, before that, PHP runs into a timeout and halts. In both cases it cases site transfer failure.
When this happens we recommend an easier, alternative method to transferring your site. Create a regular backup profile and use the "Upload to Remote FTP Server" or "Upload to Remote SFTP Server" to transfer the backup archive to the new host. As a precaution, you are advised to set the
Part size for split archives in the Archiver Engine configuration pane to 20Mb or smaller. After the backup is complete the backup file(s) will be transferred to the new server. Just upload Kickstart into it and run Kickstart. This method uses far fewer FTP connection requests than the Site Transfer Wizard, it's faster (usually: five to ten times faster!) and only requires you to upload 1 file manually.
Dale L. Brackin
Support Specialist
English: native
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!
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EST (UTC -5) (click here to see my current time in Philadelphia, PA)