Proxmox Backup Server 4.0 Beta Released – Try the New Features Today!

If you have been following along with my post from yesterday, Proxmox has released Proxmox VE Server 9 Beta just a few days ago now at the time of this writing. To go along with that release, they have also dropped Proxmox Backup Server 4.0 Beta. Like Proxmox 9 Beta, Proxmox Backup Server 4.0 Beta is chocked full of new features that will appeal to a wide range of use cases and audiences, including home lab enthusiasts, and for the enterprise alike. Let’s dive in and see what is under the covers of this latest release!

What is Proxmox Backup Server (PBS)?

In case you didn’t know, Proxmox has their own totally free backup solution for Proxmox VE Server, called Proxmox Backup Server (PBS). For those of us who come from a primarily enterprise background with solutions like VMware, we are used to having the need for enterprise backup solutions. However, with Proxmox, you have a fully supported enterprise-ready solution that is totally free! Hard to believe, but that is the case.

Granted it is encouraging to see the support from enterprise vendors with recently announced or released Proxmox compatibility, but it is equally great to know you don’t have to pay for an expensive enterprise backup solution for Proxmox if you don’t want to have to do that.

Overview of new features in Proxmox Backup Server 4.0 Beta

With the 4.0 Beta release, Proxmox has advanced the solution in many ways, including modernizing the base OS and introducing major improvements for flexibility, performance, and security.

Here’s a quick overview of the major feature highlights:

• Based on Debian 13 “Trixie”
• Kernel 6.14.8-1 (new stable default)
• ZFS 2.3.3 with live RAIDZ expansion
• S3-compatible object storage backend (tech preview)
• Improved removable datastore sync jobs
• Enhanced notifications and GUI
• Expanded support for alternative NIC naming
• Security improvements, bug fixes, and translation updates

Now, let’s break these down.

Debian 13 “Trixie” + Linux kernel 6.8

Like Proxmox VE Server 9 Beta, Proxmox has uplifted the underlying Linux operating system underneath to Debian 13 “Trixie”. This brings PBS to the very latest Debian release, which is great as it includes updated libraries, improved security defaults, and better hardware compatibility.

The Linux 6.8 kernel helps to give you additional performance and storage optimizations. This is especially helpful for high-throughput backup environments and modern storage with the latest hardware.

S3-Compatible backup storage (Tech Preview)

I think this is going to be a great new feature. Not only can you backup to native Amazon S3 in Proxmox Backup Server 4.0 Beta, you can now connect to storage systems that implement S3-compatible storage as well. Think about storage solutions that you may have heard about like MinIO and Wasabi.

A new datastore type allows you to send backup metadata and chunks to object storage, with a local cache used to reduce request volume and improve performance.

There are some limitations to be aware of such as the following:

• Each S3 datastore can only be used by a single PBS instance

However, it is noted that the data may be reused by a new instance if the original one is permanently lost. This new functionality is great as it will open up major potential for hybrid cloud workflows and cost-effective long-term retention.

ZFS 2.3.3 with live RAIDZ expansion

Storage in PBS 4.0 Beta has definitely been given some love by the developers. ZFS has been upgraded to version 2.3.3 the same as it has been in Proxmox VE Server 9.0 Beta, and supports live RAIDZ expansion. You can now add new disks to an existing RAIDZ pool without downtime. This definitely helps with a longstanding pain point in ZFS-based storage. Expanding your ZFS now will be a piece of cake in PBS 4.0.

Smarter sync for removable datastores

PBS 4.0 Beta allows you to automatically trigger sync jobs when a removable datastore is mounted. This will be a great feature for offsite rotation schemes and USB-attached backup media in edge locations.

New behavior includes:

• Sync jobs with run-on-mount flag will auto-execute upon mount
• Jobs will only run if the referenced datastore is actively mounted

This is a simple change but it is a great quality of life improvement for edge locations and offline locations that rely on these types of storage for backups.

GUI and UX enhancements

The web interface has also been polished in this release with the following enhancements to name just a few:

• Fixes for datastore creation tasks not displaying properly
• A cleaned-up consent window for OpenID Connect (OIDC) logins
• UI fixes for viewport sizing and duplicate consent text
• HttpOnly cookies for added security
• Better visibility into node services
• Fixes for services reported incorrectly like postfix

Like Proxmox VE Server 9.0, PBS 4.0 will continue to be a very intuitive interface for both newcomers to the platform as well as those that have been on Proxmox and PBS for some time now.

Improved notifications

Backup and tape jobs now default to using the notification system (notification-system mode). This is true even when created via the CLI or API. Not the following other improvements to notifications:

• You will get warnings when a mailto-user lacks an email
• Many GUI improvements for configuring notifications
• Fixes for SMTP bugs and sender quoting
• Tape job notifications have been moved to a separate tab

Garbage collection & snapshot prune improvements

The garbage collection system will now allow you to bypass the chunk cache with cache=0 setting. Chunk cache stats are also logged for monitoring and other metrics. Index file deletions mid-job are handled much more gracefully and there were fixes in some rare race conditions seen. There are other fixes included, such as:

• Snapshot forget operations that failed if notes or owner files were missing
• Sync jobs mistakenly locking source snapshots, causing backup conflicts

These changes improve reliability during cleanup and reduce edge case errors.

Installation & ISO improvements

Just like Proxmox VE Server 9.0 Beta, the installer with PBS 4.0 Beta has also been improved. The installer now includes matching CPU microcode packages enabled via non-free firmware repositories. Error handling has been improved for RAID and CIDR configurations. It also handles DHCP search domain overrides and has better feedback for failed disk and network configurations.

Support for alternate NIC names

PBS 4.0 now lets you have alternative network interface names. This includes up to 128-byte identifiers. This will be a helpful feature to help Proxmox admins have some consistency in their /etc/network/interfaces file even when primary NIC names change across kernel versions or hardware swaps.

Should you try the PBS 4.0 Beta?

I say – absolutely! Throw it on a mini PC or VM inside of a Proxmox VE Server 9.0 Beta as I know you want to try that too. I probably would say I wouldn’t run anything “production” in the home lab on it just yet until it is GA, and definitely not true production environments. However, if you are like me, I like to get my hands on the new features early so you can get familiar with the new tricks we now have access too.

Download link and other resources

Check out the following official resources for learning more about Proxmox Backup Server 4.0 Beta and downloading!

• Release notes – https://pbs.proxmox.com/wiki/index.php/Roadmap
• Download – https://enterprise.proxmox.com/iso
• Community Forum – https://forum.proxmox.com
• Bugtracker – https://bugzilla.proxmox.com
• Source code – https://git.proxmox.com