Re: [PVE-User] Analysis of free space...

[Alwin Antreich via pve-user <pve-user@lists.proxmox.com>]

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From: "Alwin Antreich" <alwin@antreich.com>
To: "Proxmox VE user list" <pve-user@lists.proxmox.com>
Subject: Re: [PVE-User] Analysis of free space...
Date: Thu, 09 Oct 2025 20:21:46 +0000
Message-ID: <83a699e14058057ed3467637dc2f2e1fa4199a08@antreich.com>

Hi Marco,


October 6, 2025 at 1:32 PM, "Marco Gaiarin" <gaio@lilliput.linux.it mailto:gaio@lilliput.linux.it?to=%22Marco%20Gaiarin%22%20%3Cgaio%40lilliput.linux.it%3E > wrote:


> 
> Mandi! Alwin Antreich via pve-user
>  In chel di` si favelave...
> 
> > 
> > Hm... I assume you're running a RAIDz1?
> > 
> root@lamprologus:~# mailto:root@lamprologus:~#  zpool status rpool-data
>  pool: rpool-data
>  state: ONLINE
> status: Some supported and requested features are not enabled on the pool.
>  The pool can still be used, but some features are unavailable.
> action: Enable all features using 'zpool upgrade'. Once this is done,
>  the pool may no longer be accessible by software that does not support
>  the features. See zpool-features(7) for details.
>  scan: scrub repaired 0B in 1 days 15:06:52 with 0 errors on Mon Sep 15 15:30:54 2025
> config:
> 
>  NAME STATE READ WRITE CKSUM
>  rpool-data ONLINE 0 0 0
>  raidz1-0 ONLINE 0 0 0
>  scsi-35000c500d2ae07db ONLINE 0 0 0
>  scsi-35000c500d2ae767f ONLINE 0 0 0
>  scsi-35000c500e24688cf ONLINE 0 0 0
>  scsi-35000c500d2af2d43 ONLINE 0 0 0
>  scsi-35000c500d2aee0df ONLINE 0 0 0
>  scsi-35000c500d2af4693 ONLINE 0 0 0
>  scsi-35000c500f9797483 ONLINE 0 0 0
>  scsi-35000c500d2ae777f ONLINE 0 0 0
>  scsi-35000c500d2af3e77 ONLINE 0 0 0
> 
> errors: No known data errors
> 
> Yep.
> 
> > 
> > See the link: https://pve.proxmox.com/pve-docs/pve-admin-guide.html#sysadmin_zfs_raid_size_space_usage_redundancy
> > 
> OK. But this can explain some data, not 20TB of not reclaimed space; and, as
> just stated, if i delete now (after that i've set discard=on on volume
> property) data, space get correctly reclaimed.
> 
The parity is calculated for data written and by the docs [0], it is 8K zvol block + 4K parity (50%). See also the openzfs docs [1].

By that calculation you'll need 512 GB for every 1 TB written. That means that the 2TB disk will use 3TB on ZFS, plus some extra.

I hope this helps.

Cheers,
Alwin

[0] https://pve.proxmox.com/pve-docs/pve-admin-guide.html#sysadmin_zfs_raid_size_space_usage_redundancy
[1] https://openzfs.github.io/openzfs-docs/Basic%20Concepts/RAIDZ.html

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