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  • Duplicati Documentation
  • Getting Started
    • Installation
    • Set up a backup in the UI
    • Running a backup
    • Restoring files
  • Detailed descriptions
    • Choosing Duplicati Type
    • Using the secret provider
      • Local providers
      • Cloud providers
      • Advanced configurations
    • Using remote management
      • Using remote control with agent
    • Migrating Duplicati to a new machine
    • Scripts
    • Sending reports
      • Monitoring with Duplicati Console
      • Sending reports with email
      • Sending Jabber/XMPP notifications
      • Sending HTTP notifications
      • Sending Telegram notifications
      • Custom message content
    • Duplicati Access Password
    • Import and export backup configurations
    • Filters in Duplicati
    • The local database
    • The server database
    • Preload settings
    • Retention settings
    • Using Duplicati with Linux
    • Using Duplicati from Docker
    • Using Duplicati with MacOS
    • Using Duplicati with Windows
    • Running a self-hosted OAuth Server
  • Using tools
    • Encrypting and decrypting files
    • Using Duplicati from the Command Line
    • Recovering from failure
    • Disaster recovery
  • Backup destinations
    • Destination overview
    • Standard based destinations
      • File Destination
      • S3-compatible Destination
      • FTP Destination
      • SFTP (SSH) Destination
      • WebDAV Destination
      • OpenStack Destination
      • Rclone Destination
      • CIFS (aka SMB) Destination
    • Provider specific destinations
      • Backblaze B2 Destination
      • Box.com Destination
      • Rackspace CloudFiles Destination
      • IDrive e2 Destination
      • Mega.nz Destination
      • Aliyun OSS Destination
      • Tencent COS Destination
      • Jottacloud Destination
      • pCloud Destination
      • Azure Blob Storage Destination
      • Google Cloud Storage Destination
      • Microsoft Group Destination
      • SharePoint Destination
      • SharePoint v2 (Graph API)
      • Amazon S3 destination
    • File synchronization providers
      • Dropbox Destination
      • Google Drive Destination
      • OneDrive Destination
      • OneDrive For Business Destination
    • Decentralized providers
      • Sia Destination
      • Storj Destination
      • TahoeLAFS destination
  • Duplicati Programs
    • TrayIcon
    • Server
    • Command Line Interface CLI
    • Service and WindowsService
    • Command Line Tools
      • AutoUpdater
      • BackendTester
      • BackendTool
      • RecoveryTool
      • SecretTool
      • SharpAESCrypt
      • Snapshots
      • ServerUtil
    • Agent
    • LICENSE
      • Duplicati Inc & Open Source
      • License Agreement
    • OAuth Server
  • SUPPORT
  • Installation details
    • Release channels and versions
      • Upgrading and downgrading
      • Downgrade from 2.1.0.2 to 2.0.8.1
    • Package options
    • Developer
  • TECHNICAL DETAILS
    • Architecture Premises
    • Understanding Backup
      • How Backup Works
      • Encryption Algorithms
      • Backup size parameters
    • Understanding Restore
      • How Restore Works
      • Disaster Recovery
    • Database versions
    • Server authentication model
    • Option formats
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  1. TECHNICAL DETAILS
  2. Understanding Backup

How Backup Works

This page describes how backups work from a high level perspective

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Last updated 6 months ago

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The core backup process is at a high level view:

  • Activate operating system snapshot (if possible)

  • Scan source folder content recursively

  • For each file

    • Read a block at a time

    • Check if the block already exists

      • Ignore if it exists

      • Add to volume if new

    • Process next block

With this core, it is possible to generate the volumes that are uploaded. Each time a block is added to a volume, the size is checked against the maximum volume size. If the limit is reached, a new volume is started, and the previous volume is processed. For a more detailed developer-oriented description, see the .

The process for a volume file is:

  • Compress file (if not done when adding a block)

  • Encrypt the file

  • Upload the file

At the end of the backup, when all files are processed, and all blocks are uploaded, a file list is uploaded that explains how to recreate all the processed files.

After the upload, a check is made to ensure that the remote storage looks as expected, and a few random volumes are downloaded to ensure the backup data is available.

If there are any retention rules active, Duplicati will then remove old lists, and possibly start to reclaim some remote storage by consolidating remote volumes.

forum post on how the backup process works