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Backup · head to head

Kopia vs Proxmox Backup Server

Kopia logo

Kopia

Backup

Open source deduplicating backup with client side encryption and a repository on almost any storage

From
Free
Rated
-
Full reviewWebsite
Proxmox Backup Server logo

Proxmox Backup Server

Backup

Deduplicating backup server for virtual machines, containers and Linux hosts, with verification built in

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Kopia space is only reclaimed when maintenance runs, and in a shared repository full maintenance is owned by one client, so if that machine goes away the repository grows for ever while every backup still reports success.; Proxmox Backup Server there is no Windows client, so physical Windows machines must be backed up by something else and the estate ends up with two backup products.
  • They diverge on capability: Kopia covers Content defined chunking, Proxmox Backup Server covers Deduplicated chunk store.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which Kopia and Proxmox Backup Server actually diverge.

Attributes where Kopia and Proxmox Backup Server differ
AttributeKopiaProxmox Backup Server
PlatformsLinux, macOS, Windows, DockerLinux

Identical on both: starting price (Free), pricing model (Open source, no licence fee), free tier (Yes), user rating (Not yet rated), category (Backup).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Kopia

  • Content defined chunking
  • Global deduplication
  • Pack blobs
  • Desktop and command line
  • Repository verification

Only in Proxmox Backup Server

  • Deduplicated chunk store
  • Incremental guest backups
  • Verification jobs
  • Remote sync
  • Live restore and file level restore

Both cover

  • Client side encryption

What people use each for

The jobs each tool is most often brought in to do.

Kopia

  • Backing up laptops and workstations to cheap object storage with a desktop interface rather than a cron jobnot Proxmox Backup Server
  • Deduplicating backups of several similar machines into one repository so common content is stored oncenot Proxmox Backup Server
  • Replacing a chunk based tool whose per object charges made a cheap bucket expensivenot Proxmox Backup Server
  • Keeping an encrypted offsite copy where the storage provider must never be able to read the contentsnot Proxmox Backup Server

Proxmox Backup Server

  • Backing up a Proxmox VE cluster with incremental block level backups of running guestsnot Kopia
  • Replacing a backup product whose licence is priced per socket or per terabyte on a virtualisation estatenot Kopia
  • Proving backup integrity on a schedule rather than discovering corruption during a restorenot Kopia
  • Keeping an encrypted second copy on a remote server or on tape without a third party servicenot Kopia

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Kopia

  • Space is only reclaimed when maintenance runs, and in a shared repository full maintenance is owned by one client, so if that machine goes away the repository grows for ever while every backup still reports success.
  • The repository format has changed across versions and mixing client versions against one repository is discouraged, so a fleet must be upgraded together rather than machine by machine.
  • There is no central orchestration or reporting for many machines, so monitoring a fleet means building your own alerting around exit codes.
  • Restoring many small files is slower than the backup was, because content must be reassembled from pack blobs, and this is rarely tested until the day it matters.
  • Encryption is client side with no escrow, so a lost repository password means the data is unrecoverable and there is no vendor to appeal to.

Proxmox Backup Server

  • There is no Windows client, so physical Windows machines must be backed up by something else and the estate ends up with two backup products.
  • The datastore is millions of small chunk files, so it needs storage with real input and output capability and performs poorly on a single spinning disk or an SMB or NFS share.
  • Deduplication is per datastore, so splitting workloads across datastores for retention or tenancy reasons multiplies the storage those workloads consume.
  • Garbage collection depends on file access time semantics on the underlying filesystem, so a datastore mounted with the wrong options can fail to reclaim space or, worse, behave unpredictably.
  • Subscriptions are priced per CPU socket per year, so a backup server consolidated onto fewer larger dual socket machines pays twice per host for the supported repository.

Pricing, plan by plan

Kopia

Free
  • KopiaFree
    • Full functionality, no data limit
    • Desktop application included
    • Any supported storage back end

Proxmox Backup Server

Free
  • No subscriptionFree
    • Full functionality with no capacity limit
    • Community package repository
    • Community forum support
  • Subscription$undefined/year
    • Priced per CPU socket per year
    • Access to the enterprise package repository
    • Vendor support tickets

Which should you pick?

Choose Kopia if

  • You need content defined chunking.
  • You want to start without paying.
  • You work on Linux, macOS, Windows, Docker.
  • You also want global deduplication.
Kopia review

Choose Proxmox Backup Server if

  • You need deduplicated chunk store.
  • You want to start without paying.
  • You work on Linux.
  • You also want incremental guest backups.
Proxmox Backup Server review

Questions people ask

Is Kopia or Proxmox Backup Server better?
Neither clearly leads. Kopia starts at Free and Proxmox Backup Server at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Kopia or Proxmox Backup Server?
Kopia starts at Free and Proxmox Backup Server at Free.
Does Kopia or Proxmox Backup Server run on more platforms?
Kopia runs on Linux, macOS, Windows, Docker. Proxmox Backup Server runs on Linux.
Can I use Kopia for free?
Both have a free tier, so you can try either at no cost before committing.
What is Kopia best used for?
Kopia is most often used for backing up laptops and workstations to cheap object storage with a desktop interface rather than a cron job, deduplicating backups of several similar machines into one repository so common content is stored once, replacing a chunk based tool whose per object charges made a cheap bucket expensive, keeping an encrypted offsite copy where the storage provider must never be able to read the contents. Of those, backing up laptops and workstations to cheap object storage with a desktop interface rather than a cron job and deduplicating backups of several similar machines into one repository so common content is stored once are not what Proxmox Backup Server is typically brought in for.
What can Kopia do that Proxmox Backup Server cannot?
Kopia covers Content defined chunking, Global deduplication, Pack blobs, Desktop and command line. Proxmox Backup Server covers Deduplicated chunk store, Incremental guest backups, Verification jobs, Remote sync. Both handle Client side encryption.

Answered from the vendors’ own pages

Kopia: Is a partly corrupt repository still restorable?

Partly. Deduplication means one damaged pack blob affects every snapshot referencing its contents, but unaffected files still restore. Run verification regularly rather than assuming.

Proxmox Backup Server: Can it back up machines that are not on Proxmox?

Linux hosts yes, through the client, at file level. Other hypervisors and physical Windows machines are outside its scope.

Kopia: How does it compare with restic?

Similar guarantees, with packing that behaves better on per operation billing, a desktop interface, and compression enabled by default.

Proxmox Backup Server: Is a subscription required?

No. Without one you use the community repository and forum support. The subscription buys the tested enterprise repository and vendor tickets.

Kopia: Do I need to run maintenance manually?

It is scheduled automatically by default, but you must ensure the client that owns full maintenance keeps running, otherwise deleted snapshots never free space.

Proxmox Backup Server: How do I know a backup will restore?

Run verification jobs. They re-read the stored chunks and mark snapshots verified or failed, which is stronger evidence than a successful backup log.

Kopia: Can several machines share one repository?

Yes, and that is where deduplication pays off, but they should run compatible versions and only one owns full maintenance.

Proxmox Backup Server: What storage should the datastore be on?

Local disks, ideally with ZFS and enough input and output capacity for many small files. Network shares are supported but routinely disappointing.

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