Plesk Backup to remote FTP server fails: Unable to resume an interrupted upload

Symptoms

• A Plesk Backup to a remote FTP server fails with one of the following messages present in its backup log:

  INFO: Seek out of scope of stream cache Unable to resume an interrupted upload: Seek out of scope of a stream cache (current cache size: 6 MB, cached data size: 6 MB, required data size: 7 MB): The connectivity problem: (55) Failed sending data to the peer: Last FTP request: STOR backup_2211150004.tar: Last FTP response: 150 Ok to send data
  INFO: pmm-ras finished. Exit code: 1
  ERR [panel] Unable to create the remote backup: Unable to resume an interrupted upload: Seek out of scope of a stream cache (current cache size: 6 MB, cached data size: 6 MB, required data size: 7 MB
  ): The connectivity problem: (55) Failed sending data to the peer: Last FTP request: STOR backup_2211150004.tar: Last FTP response: 150 Ok to send data

  [2024-11-12 05:51:57.998|1589572] INFO: Requested data is out of the cached data (requested offset: %1%, stream offset: %2%, cache size: %3%, cached data size: %4%)
  ...
  [2024-11-12 05:52:02.250|1589572] INFO: TransportError Transport error: Unable to resume an interrupted upload: Requested data is out of the cached data (current cache size: 5 MB, cached data size: 5 MB, required data size: 5 MB): The connectivity problem: (55) Failed sending data to the peer: Last FTP request: APPE
  backup_2411120315.tar: Last FTP response: 150 Opening BINARY mode SSL data connection
  [2024-11-12 05:52:02.250|1589355] DEBUG [panel] File domains/example.com/backup_user-data_2411120315.tzst exported (3241900083/-269220214453/73)
  [2024-11-12 05:52:02.253|1589572] INFO: pmm-ras finished. Exit code: 1
  ...
  [2024-11-12 05:52:02.378|1589355] ERR [panel] PleskbackupAgentExceptionExportFailed: Unable to create the remote backup: Transport error: Unable to resume an interrupted upload: Requested data is out of the cached data (current cache size: 5 MB, cached data size: 5 MB, required data size: 5 MB): The connectivity problem: (55) Failed sending data to the peer: Last FTP request: APPE backup_2411120315.tar: Last FTP response: 150 Opening BINARY mode SSL data connection

Cause

The currently configured stream cache size is insufficient and needs to be increased.

Resolution

1. Connect to the server via SSH

2. Edit the Plesk panel.ini file and add the following cache directive in the [pmm] section (feel free to increase the value shown below as necessary):

   streamCacheSize = 1024