PBS, calculate size of tape backup

May 6, 2021
53
4
13
Bern, Switzerland
Hi

Found these two links about the possibilities to calculate the size of backups.
https://forum.proxmox.com/threads/real-size-of-diskspace-used-in-backups.102664/
https://forum.proxmox.com/threads/how-to-get-the-exactly-backup-size-in-proxmox-backup.93901/

Our challenge is to not use more than two tapes on a full backup due to limitations of the export slots and onsite staff.

We see that roughly 16 TB are fitting on one LTO-9. But it seems to change due to? Backups not getting split at an end of a tape? Anything else?
Oct, 25th tape 0 = 15.96 TB, tape 1 = 15.97 TB
Nov, 1st, tape 0 = 16.39 TB, tape 1= 13.68 TB
Nov, 8th, tape 0 = 16.39 TB, tape 1 =13.87 TB
Nov, 15th tape 0 = 16.39 TB, tape 1 = 14.71 TB
Nov, 22th tape 0 = 16.39 TB, tape 1 = 15.65 TB
Nov, 29th tape 0 = 15.08 TB, tape 1 = 15.26 TB, tape 2 = 1.66 TB

We could use exclude filters to avoid some of the larger and not that essential vms, but we would be glad to predict the size somehow.
Any hint?

Regards, Urs
 

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