Offsite backup for Windows servers
A client on the server, a Proxmox Backup Server datastore on our side, and nothing else to build. VSS snapshots, optional encryption with a key that stays with you, signed binaries.
Who it is for: Windows servers, no Proxmox
You run Windows servers (files, applications, SQL Server), physical or virtualised on Hyper-V, VMware or at a hosting provider, and you want a copy of their data outside your walls. You do not use Proxmox VE, and you do not want to build your own Proxmox Backup Server either.
That is the case this page covers: the Windows server sends its own backups to a Nimbus datastore. No hypervisor to change, no backup server to run, no gateway in between. Your servers run Linux? See offsite Linux server backup. Your VMs run on Proxmox VE? They go through offsite Proxmox backup, with no client to install in the VMs.
How it works
Nimbus Backup is a free, open source (GPL-3.0) Windows client that we maintain on top of Tiziano Bacocco's proxmoxbackupclient_go project. The current version is 0.4.2 (12 October 2026).
Your Nimbus datastore
You pick the volume and the plan. We create the Proxmox Backup Server datastore and the access token the client will use.
The Nimbus Backup client on the server
The signed MSI installer sets up the interface and a Windows service (LocalSystem) that runs scheduled backups, even after a reboot.
Folders, schedule, exclusions
You choose the folders, the time and the exclusions. Windows system folders (pagefile.sys, System Volume Information…) are excluded automatically.
Upload, then a restore test
The first upload sends everything, later ones only new chunks. Restore a folder right after the first backup: it is the only way to know it works.
Installation, configuration import and scheduling are covered in the tutorial: step-by-step Windows backup client setup.
What is backed up, and consistency (VSS)
The client reads data from a VSS (Volume Shadow Copy) snapshot: open files are backed up as they were at the moment of the snapshot, not half written.
Folders
- One VSS snapshot for a whole multi-folder backup
- Several folders uploaded in parallel (configurable)
- File and folder exclusions
- A large first upload can be split into smaller backups that resume after a cut (option)
- Shadow copies deleted as soon as the backup ends, so they do not pile up on the disk
Whole disks (beta)
Since 0.4.0, the client can also back up whole physical disks, picked by their identity. This mode is still in beta: 0.4.1 and 0.4.2 fixed real defects in it.
Test it on your server before you make it the basis of a recovery plan.
Databases: go through a native backup
A VSS snapshot makes the files readable, not a SQL Server database you can be sure to restore. Schedule a native backup (.bak) and back up its folder with Nimbus Backup.
Volumes, durations and deduplication ratio measured on a real server: first 1 TB Windows backup: case study.
Client-side encryption and signed binaries
Optional encryption, your key
Since 0.4.1, the client can encrypt backups on the server before upload (AES-256-GCM), if you enable it. The format is the one of proxmox-backup-client: on every build, continuous integration checks that a backup encrypted by Nimbus Backup restores with the official client, and the other way round.
We do not hold the key. If it is lost, the backups are unreadable, for you as for us: keep a copy away from the server.
Binaries signed by RDEM SYSTEMS
Since 0.4.1, NimbusBackup.exe, its service and the NimbusBackup.msi installer are signed (Authenticode, Azure Artifact Signing) by RDEM SYSTEMS. The command-line tools are not signed yet.
Each release publishes its SHA-256 checksums and its VirusTotal report. What this release brings: what 0.4.1 changes.
Restoring
You restore from the Windows server, in the client, without having to ask us anything.
Browse backups
Each snapshot can be browsed in the interface, with a fast search through the file catalog.
Files and folders
Restore a file, a folder or a whole snapshot, to its original location or elsewhere, with NTFS permissions.
Encrypted backups
Restore, search and browse decrypt with your key, on the server.
From the PBS web interface
For an unencrypted backup, the datastore's web interface also lets you download files from another computer.
How long a restore takes depends on the volume and your download bandwidth: we measure it with you during a test, we do not promise it.
Retention and offsite copies
An account that cannot delete. The token installed on your server can write backups, not erase them. Old backups are removed by retention, on the Nimbus side.
Default retention: last 3, 7 daily, 4 weekly, 3 monthly. We adjust it on request; to see what another retention costs in space, use the retention simulator.
An offline copy, if you want one. The AirGapped Drive plan adds, on top of the online copy, unplugged disks with a monthly rotation: at any time, two months of offline backups.
What makes a copy truly offsite, and the steps for each type of machine: the offsite backup guide.
Pricing: per TB stored, not per server
From €12 excl. VAT/TB/month on Single Drive, €34 excl. VAT/TB/month on AirGapped Drive with the offline copy. The number of Windows servers backing up to the datastore does not change the price, and the client costs nothing.
Over 3 TB: on quote, with the provisioning lead time confirmed in the quote (usually under a week). Hosted in the European Union, in France on request.
Configure your backupWindows server FAQ
Take your Windows servers offsite
Pick the volume and the plan, install the client, restore a folder to check. A question before you start? 15-minute tech call, no commitment.