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

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

[Marco Gaiarin]

We have an PVE8 server, on clustered, with 66TB of disk storage and (for
now) a single VM; volumes have all 'discard' option enabled, and the VM
(RH8) support and have trim enabled.

We moved around some data between volumes, and now we have 20TB used in the
VM, and 56TB used on the zfs pool that host that volumes.

Clearly we have done some manual 'trim' to be sure, but nothing changed (or,
better, some space get reclaimed but not what we expect).


There's some tool/methodology to find where data get stuck, and how?


Thanks.

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

[Gilou]

Le 17/09/2025 à 15:27, Marco Gaiarin a écrit :
> 
> We have an PVE8 server, on clustered, with 66TB of disk storage and (for
> now) a single VM; volumes have all 'discard' option enabled, and the VM
> (RH8) support and have trim enabled.
> 
> We moved around some data between volumes, and now we have 20TB used in the
> VM, and 56TB used on the zfs pool that host that volumes.
> 
> Clearly we have done some manual 'trim' to be sure, but nothing changed (or,
> better, some space get reclaimed but not what we expect).
> 
> 
> There's some tool/methodology to find where data get stuck, and how?
Hi,

What's the underlying storage? local zfs?
Does it have thin provisioning / sparse enabled?

You can check that forum post: 
https://forum.proxmox.com/threads/zfs-enable-thin-provisioning.41549/

Also inside the VM, make sure that all the stack is discard aware, LVM, 
filesystem and all..

Regards,
Gilou

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

[Alwin Antreich via pve-user]

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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, 18 Sep 2025 13:44:04 +0000
Message-ID: <63783ca5c3f39fab913e615393ceea9c55bf147e@antreich.com>

Hi Marco,


September 17, 2025 at 3:27 PM, "Marco Gaiarin" <gaio@lilliput.linux.it mailto:gaio@lilliput.linux.it?to=%22Marco%20Gaiarin%22%20%3Cgaio%40lilliput.linux.it%3E > wrote:


> 
> We have an PVE8 server, on clustered, with 66TB of disk storage and (for
> now) a single VM; volumes have all 'discard' option enabled, and the VM
> (RH8) support and have trim enabled.
> 
> We moved around some data between volumes, and now we have 20TB used in the
> VM, and 56TB used on the zfs pool that host that volumes.
> 
> Clearly we have done some manual 'trim' to be sure, but nothing changed (or,
> better, some space get reclaimed but not what we expect).
> 
> There's some tool/methodology to find where data get stuck, and how?
> 
Are you running EXT4 on the guest?
https://forum.proxmox.com/threads/help-with-trim-on-virtio-scsi-single.123819/post-542552

Cheers,
Alwin

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

[Marco Gaiarin]

Mandi! Gilou
  In chel di` si favelave...

> What's the underlying storage? local zfs?
> Does it have thin provisioning / sparse enabled?

Yes, storage is ZFS, and 'Thin provision' is enabled.


> Also inside the VM, make sure that all the stack is discard aware, LVM, 
> filesystem and all..

VM is an RH8, so pretty new, so have full support for discard. And, as just
stated, trimming effectively free some TB of data, but not what we expect...

Effectively the VM use LVM, but looking around seems to me that discard is
'transparent' against LVM, eg, there's no need/way to 'enable' or 'disable'
it... if it is supported by the underlying storage...

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

[Marco Gaiarin]

Mandi! Alwin Antreich via pve-user
  In chel di` si favelave...

> Are you running EXT4 on the guest?
> https://forum.proxmox.com/threads/help-with-trim-on-virtio-scsi-single.123819/post-542552

I think is XFS. I'll check.

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

[Marco Gaiarin]

Mandi! Gilou
  In chel di` si favelave...

> You can check that forum post: 
> https://forum.proxmox.com/threads/zfs-enable-thin-provisioning.41549/

Uh, wait... effectively we forgot to enable 'discard' on volumes, and we have
enabled afterward (but rebooted the VM).

I'll check refreservation property and report back.

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