I've been successfully creating TAR backups (about 12 GB), but after switching to ZIP the backups fail all the time. A backup file is uploaded to S3 with a size of 4.01 GB. I suspect the reason is that BackWPup doesn't split the archive to compensate for the 4 GB ZIP limit and it doesn't use ZIP64 either.
Here's the log:
[INFO] BackWPup 3.3; A project of Inpsyde GmbH
[INFO] Log Level: Normal (translated)
[INFO] BackWPup job: Daily to S3
[INFO] Logfile is: backwpup_log_08fe03_2016-04-01_03-00-07.html
[INFO] Backup file is: xxx_2016-04-01_03-00-07.zip
[01-Apr-2016 03:00:07] 1. Try to backup database …
[01-Apr-2016 03:00:08] Connected to database xxx on localhost
[01-Apr-2016 03:01:05] Added database dump "xxx.sql" with 181,10 MB to backup file list
[01-Apr-2016 03:01:05] Database backup done!
[01-Apr-2016 03:01:05] 1. Trying to make a list of folders to back up …
[01-Apr-2016 03:01:10] Added "wp-config.php" to backup file list
[01-Apr-2016 03:01:10] 839 folders to backup.
[01-Apr-2016 03:01:10] 1. Trying to generate a file with installed plugin names …
[01-Apr-2016 03:01:10] Added plugin list file "XYZ.pluginlist.2016-04-01.txt" with 4,91 kB to backup file list.
[01-Apr-2016 03:01:10] 1. Trying to generate a manifest file …
[01-Apr-2016 03:01:10] Added manifest.json file with 6,71 kB to backup file list.
[01-Apr-2016 03:01:10] 1. Trying to create backup archive …
[01-Apr-2016 03:01:10] Compressing files as ZipArchive. Please be patient, this may take a moment.
[01-Apr-2016 03:32:04] WARNING: ZipArchive::close(): Invalid or unitialized Zip object
[01-Apr-2016 03:32:04] ERROR: ZIP archive cannot be closed correctly.
[01-Apr-2016 03:32:05] ERROR: Cannot create backup archive correctly. Aborting creation.
[01-Apr-2016 03:32:07] 2. Trying to create backup archive …
[01-Apr-2016 03:32:07] Compressing files as ZipArchive. Please be patient, this may take a moment.
[01-Apr-2016 04:05:41] WARNING: ZipArchive::close(): Invalid or unitialized Zip object
[01-Apr-2016 04:05:41] ERROR: ZIP archive cannot be closed correctly.
[01-Apr-2016 04:05:42] ERROR: Cannot create backup archive correctly. Aborting creation.
[01-Apr-2016 04:05:43] 3. Trying to create backup archive …
[01-Apr-2016 04:05:43] Compressing files as ZipArchive. Please be patient, this may take a moment.
[01-Apr-2016 04:37:53] WARNING: ZipArchive::close(): Invalid or unitialized Zip object
[01-Apr-2016 04:37:53] ERROR: ZIP archive cannot be closed correctly.
[01-Apr-2016 04:37:54] ERROR: Cannot create backup archive correctly. Aborting creation.
[01-Apr-2016 04:37:54] ERROR: Step aborted: too many attempts!
[01-Apr-2016 04:37:54] 1. Trying to send backup file to S3 Service …
[01-Apr-2016 04:37:57] Connected to S3 Bucket "aasbackupeu" in eu-west-1
[01-Apr-2016 04:37:57] Checking for not aborted multipart Uploads …
[01-Apr-2016 04:37:57] Starting upload to S3 Service …
[01-Apr-2016 04:43:27] Backup transferred to XXX.
[01-Apr-2016 04:43:28] One file deleted on S3 Bucket.
[01-Apr-2016 04:43:28] One old log deleted
[01-Apr-2016 04:43:28] ERROR: Job has ended with errors in 6201 seconds. You must resolve the errors for correct execution.