Update: This appears to be a conflict between the threads. If I set workers to 1, it downloads the files completely. No 0 byte files.
Previously:
In addition to the above problem, even the "successful" sync created 0 byte files almost half the time. For example, the _db_backups/DATABASE_NAME_09.sql.gz file was 0 bytes due to "550 Can't open _db_backups/DATABASE_NAME_09.sql.gz: No such file or directory". Other files in the same directory downloaded perfectly. Average size was 140KB. There's no reason to believe the failed files were being accessed or written to at the time. Downloading the _09 file manually with FTP Voyager worked fine.
The ftp server identifies itself as:
220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
Here's the log of the _09 file:
[03] Fri 21Jun13 15:10:50 - Receiving: _db_backups/DATABASE_NAME_09.sql.gz -> D:\shared\backup\websites\godaddy\_db_backups\DATABASE_NAME_09.sql.gz
[05] Fri 21Jun13 15:10:50 - PASV
[06] Fri 21Jun13 15:10:50 - 227 Entering Passive Mode (72,167,183,26,204,212)
[03] Fri 21Jun13 15:10:50 - Opening passive mode data connection to 72.167.183.26, port 52436.
[06] Fri 21Jun13 15:10:50 - 226-File successfully transferred
[06] Fri 21Jun13 15:10:50 - 226 0.691 seconds (measured here), 203.42 Kbytes per second
[05] Fri 21Jun13 15:10:50 - RETR _db_backups/DATABASE_NAME_09.sql.gz
[06] Fri 21Jun13 15:10:50 - 550 Can't open _db_backups/DATABASE_NAME_09.sql.gz: No such file or directory
[04] Fri 21Jun13 15:10:50 - Download of "D:\shared\backup\websites\godaddy\_db_backups\DATABASE_NAME_09.sql.gz" failed.
Here's a portion of my local directory after the scheduled sync (database name changed slightly):
06/14/2013 02:20 AM 0 DATABASE_NAME_13.sql.gz
06/15/2013 02:20 AM 151,519 DATABASE_NAME_14.sql.gz
06/16/2013 02:20 AM 0 DATABASE_NAME_15.sql.gz
06/17/2013 02:20 AM 154,340 DATABASE_NAME_16.sql.gz
06/18/2013 02:20 AM 0 DATABASE_NAME_17.sql.gz
06/19/2013 02:20 AM 151,398 DATABASE_NAME_18.sql.gz
06/20/2013 02:20 AM 0 DATABASE_NAME_19.sql.gz
06/21/2013 02:20 AM 151,452 DATABASE_NAME_20.sql.gz
06/21/2013 02:20 PM 0 DATABASE_NAME_21.sql.gz
05/23/2013 02:20 AM 0 DATABASE_NAME_22.sql.gz
05/24/2013 02:20 AM 148,529 DATABASE_NAME_23.sql.gz
05/25/2013 02:20 AM 151,831 DATABASE_NAME_24.sql.gz
05/26/2013 02:20 AM 0 DATABASE_NAME_25.sql.gz
05/27/2013 02:20 AM 151,699 DATABASE_NAME_26.sql.gz
05/28/2013 02:20 AM 0 DATABASE_NAME_27.sql.gz
05/29/2013 02:20 AM 0 DATABASE_NAME_28.sql.gz
05/30/2013 02:20 AM 147,737 DATABASE_NAME_29.sql.gz
05/31/2013 02:20 AM 0 DATABASE_NAME_30.sql.gz
06/01/2013 02:20 AM 147,818 DATABASE_NAME_31.sql.gz
02/21/2013 02:57 PM 55,786,017 dbfiotdbinaryboy.sql
02/21/2013 02:59 PM 180 db_backup.sh
35 File(s) 58,291,510 bytes
2 Dir(s) 565,737,238,528 bytes free
D:\shared\backup\websites\godaddy\_db_backups>