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Date: Fri, 8 Oct 2021 07:02:55 +0200 (CEST)
From: Dietmar Maurer <dietmar@proxmox.com>
To: Proxmox VE user list <pve-user@lists.proxmox.com>,
 =?UTF-8?Q?St=C3=A9phane_Caminade?= <stephane.caminade@ias.u-psud.fr>
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Subject: Re: [PVE-User] backup to PBS: unable to acquire lock on snapshot
 directory
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> No one has encountered a similar problem?

I guess I also saw this when running sync jobs and backups in parallel.
Do you run any sync jobs during backup?