The Proxmox community has officially released the beta version of Proxmox Backup Server 4.0, ushering in a new era for its enterprise-grade backup solution. Built on Debian 13 “Trixie”, this release includes the Linux 6.14.8 kernel and OpenZFS 2.3.3, introducing long-awaited support for RAID-Z expansion without downtime.
S3-Compatible Storage: A Big Step Toward Hybrid Cloud
One of the most anticipated features is the S3-compatible object storage backend (in technology preview), allowing Proxmox Backup Server to connect with external storage providers using S3 APIs. This addition enables flexible and scalable backup strategies across public and private cloud environments.
The new S3 datastore includes a local cache to reduce latency and minimize the number of operations sent to the remote storage. However, note that each Proxmox instance must have its own datastore, as sharing across multiple servers is not supported.
ZFS 2.3.3: Online RAID-Z Expansion
With ZFS 2.3.3, administrators can now add disks to existing RAID-Z pools without shutting down services, a critical improvement for those needing flexible and scalable storage without compromising data integrity.
Improved Web Interface and Smarter Notifications
The web interface has received numerous enhancements, improving task management, service visibility, and multilingual support. Key improvements include:
- HttpOnly cookies for improved session protection.
- Expanded language support, including Czech, Arabic, Korean, Ukrainian, and Spanish.
- A redesigned OIDC consent dialog to avoid redundancy and viewport overflow.
Notification management has also been refined: the system now warns if a user without an email address is set to receive alerts, improves SMTP sender formatting, and sets notification-system as the default mode for new jobs.
Enhanced Sync Jobs, Tape Support, and CLI Usability
Sync jobs can now automatically run when a removable datastore is mounted. The release also fixes issues related to forgetting snapshots and improves garbage collection performance and logging.
Tape backup compatibility has been enhanced, especially for environments that prevent applications from changing encryption settings at the tape level.
CLI tools now provide clearer error messages and input validation, helping system administrators troubleshoot more efficiently.
Installation and Upgrade Considerations
The installation ISO now includes the appropriate CPU microcode package, improving security from the first boot. This also means that the non-free-firmware repository is enabled by default.
This is a beta release and should not be used in production environments. Users can upgrade from Proxmox Backup Server 3.4 via apt and will be able to upgrade from beta to stable when the final release becomes available.
To try the beta version, add the test repository:
deb http://download.proxmox.com/debian/pbs trixie pbs-test
Code language: JavaScript (javascript)Implications for Enterprises and Backup Providers
With the addition of S3-compatible storage and online RAID-Z expansion, Proxmox Backup Server 4.0 strengthens its position as a competitive open-source alternative in the backup space. These features make it a compelling option for organizations looking for flexible, hybrid, and efficient backup solutions.
The Proxmox team encourages the community to test this beta, report bugs, and share feedback via the official forum or bug tracker.
With this update, Proxmox continues to expand its open-source ecosystem for virtualization and backup, equipping professionals with powerful, scalable, and resilient tools in a rapidly evolving IT landscape.
