Replication and upgrade

This page explains how to replicate the content of one instance of Orthanc to another instance of Orthanc. This is useful to upgrade between versions of the database schema, or to create mirrored DICOM servers.

Upgrade the database schema

As explained elsewhere in the Orthanc Book, successive versions of Orthanc might use a different version of the database schema. If this happens, Orthanc will refuse to start (with an explicit message in its logs), to let the user decides whether she actually wants to upgrade the database.

At this point, the user could indeed choose to modify its configuration file in order to create a new database elsewhere on the filesystem (if using the default SQLite backend), or on the database management system (e.g. if using PostgreSQL or MySQL/MariaDB). This is important to let the user experiment a new version of Orthanc, while keeping the older version up and running.

If you decide to upgrade the database schema, you have to apply the following 3 steps:

  1. If not done yet, stop the running Orthanc service:
  2. Manually call Orthanc with the --upgrade command-line option, and point to your configuration file:
    • Under Microsoft Windows, Orthanc.exe c:/Orthanc/ --upgrade.
    • Under Debian, use sudo /usr/sbin/Orthanc /etc/orthanc/ --upgrade.
  3. Once the upgrade process is over, restart the Orthanc service:

Important remarks:

  • Orthanc is now considered as stable, which means that no upgrade in the database schema should occur in the near future.
  • Depending on the size of the Orthanc database, upgrading the database schema might take time, as this operation implies re-reading all the DICOM instances from the disk.
  • In the case of the official Debian and Fedora packages, the default location of the database changes with the version of its schema. For instance, DB schema version 6 will be stored in /var/lib/orthanc/db-v6/. If upgrading the package (and if the configuration files are purged), a new database will automatically be created on the disk. Old data can be recovered either by changing the configuration in /etc/orthanc/ to point to the previous location of the database then using --upgrade as written above, or by using the instructions for replication below.

Direct access to the filesystem

The most direct way to replicate an instance of Orthanc consists in using the ImportDicomFiles script of the Orthanc distribution. This process can also be used to restore the content of an Orthanc server after a corruption of its database.

For instance, the following command would recursively explore the content of the OrthancStorage folder (where Orthanc stores its DICOM files by default), and send each DICOM file inside this folder to the instance of Orthanc whose REST API is listening on http://192.168.0.2:8042:

$ python ImportDicomFiles.py 192.168.0.2 8042 OrthancStorage

This method will only succeed if:

  • The source Orthanc uses the default storage area on the filesystem (i.e. the source Orthanc does not store its DICOM files using one of the “storage area plugins”, such as for PostgreSQL or MySQL/MariaDB - but it’s OK for the source of Orthanc to use any of the “index plugins”),
  • You have command-line access to the source Orthanc, and
  • The transparent Compression of the DICOM instances is disabled (cf. option StorageCompression in the configuration file).

Important remark: Because of the way Orthanc stores its database on the filesystem, it is entirely normal if the ImportDicomFiles.py script ends by saying that only half of the DICOM files were properly sent. This is because the JSON summaries are not DICOM files, and are thus rejected by the target Orthanc server. More information are available on the discussion group.

Generic replication

If you cannot use the first method, you can use the Replicate script of the Orthanc distribution. This script will use the REST API of both the source and target instances of Orthanc. For instance:

$ python Replicate.py http://orthanc:password@localhost:8042/ http://192.168.0.2/

Obviously, contrarily to the first method, the source instance of Orthanc must be up and running during the replication.