How do backups to remote storage (FTP or cloud) work on a server with Plesk?

Question

How do backups to remote storage (FTP or cloud) work?

Answer

Starting from Plesk Onyx 17.5, when a backup is configured to be created on remote storage, Plesk does not create a full local copy of it. Instead, Plesk transfers the backup in parts:

1. First, a backup file of the largest Plesk domain service (database, mailbox, website web content) is created locally as a temporary archive in /var/lib/psa/dumps.

2. Then this created archive is transferred to remote storage by parts of 100MB without additional compression;

3. Simultaneously with transferring the backup to the remote storage, creation of a new archive is starting;

4. Backups are uploaded into the single file backup_<YYMMDDHHmm>.tar on the remote storage (if multivolume backup is no selected);
   

   The information on how files are organized inside the archive could be found here

   Note: If the One Drive remote storage is used, backup files are split into parts according 'writeBufferSize', because the OneDrive does not support streaming upload

5. After the archive has been uploaded to remote storage, it is removed from the Plesk server.

6. Backup manager signs remote backups and do not allow to restore backups with invalid signatures by default.

Note: Since parts of backup files are created simultaneously, it is good practice to have free space equal at least to half of the full backup size. But minimum free disk space should be equal to the size of two largest subscriptions on the server.

The following resources on the remote storage are affected during the backup creation:

• Inbound traffic on the remote storage equals to the size of the uploaded backups.
• Outbound traffic is insignificant and is used for checking the structure of uploaded backups.
• Consumed disk space quals to the size of the uploaded backups.
• Files are uploaded into the remote storage during the execution of a single durable operation.