# Calculate Proxmox tape retention from the media allocation policy

> Work out the tape retention start event as well as its configured duration.

- Canonical URL: https://update.dsesecurity.com/updates/calculate-proxmox-tape-retention-from-the-media-allocation-policy/
- Publisher: Detection Systems & Engineering (DSE Security)
- Author: DSE Security Editorial Team
- Published: 2026-10-15T13:33:00+00:00
- Modified: 2026-10-15T13:36:16+00:00
- Last reviewed by DSE: 2026-10-15
- Resource type: Guide
- DSE priority: Information
- Topics: Business Continuity, IT
- Reading time: 2 minutes

## What you need to know

Work out the tape retention start event as well as its configured duration.

## Potentially affected

This applies to Proxmox Backup Server's documented tape media-set policies. It addresses the effective retention clock and restore dependency, not legal retention advice or a guaranteed restore duration.

## DSE recommendation

DSE recommends writing worked calendar examples for the exact allocation and retention combination before assigning cartridges to the pool.

## Article

Work out the tape retention start event as well as its configured duration.

## Source facts

Proxmox Backup Server tape retention begins at different points depending on media-set allocation. Continuing an existing media set starts its retention period when a newer set exists. Always creating a new set starts the clock at that set’s creation. Calendar-based allocation uses the next set’s creation or the next scheduled allocation event when no newer set exists. Large media sets also create restore dependencies across their tapes; even a single-VM restore can require data from all tapes in the set.

Source: [Proxmox Backup Server — Tape Backup](https://pbs.proxmox.com/docs/tape-backup.html).

## Applicability

This applies to Proxmox Backup Server’s documented tape media-set policies. It addresses the effective retention clock and restore dependency, not legal retention advice or a guaranteed restore duration.

## DSE recommendation

DSE recommends writing worked calendar examples for the exact allocation and retention combination before assigning cartridges to the pool. Include a missed job or an off-site tape in that review so the team understands when reuse becomes possible. Keep media-set membership with the vault inventory, and have the recovery owner identify the complete set needed for a rehearsal. Avoid approving a policy solely from its retention-duration label without checking the event that starts that duration.

## Verification

Using disposable media or a supported test setup, compare recorded set creation and allocation events with the calculated retention start. Rehearse locating the complete media set for a selected recovery point. Retain expected reuse dates and any missing-tape dependencies before adopting the production rotation.

## Official reference

[Proxmox Backup Server — Tape Backup](https://pbs.proxmox.com/docs/tape-backup.html). Reviewed October 15, 2026.

## Primary reference

- Name: Proxmox Backup Server — Tape Backup
- Authority: pbs.proxmox.com
- URL: https://pbs.proxmox.com/docs/tape-backup.html
- Source publication date: Not stated by the source

## Citation and use

Preferred citation: “Calculate Proxmox tape retention from the media allocation policy,” DSE Security, https://update.dsesecurity.com/updates/calculate-proxmox-tape-retention-from-the-media-allocation-policy/
Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/
Usage and citation policy: https://update.dsesecurity.com/usage/
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