Re: [pve-devel] Unable to create persistent dirty-bitmap

["DERUMIER, Alexandre via pve-devel" <pve-devel@lists.proxmox.com>]

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From: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>
To: "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>, "Prashant.Gamepatil@arctera.io" <Prashant.Gamepatil@arctera.io>
Subject: Re: Unable to create persistent dirty-bitmap
Date: Tue, 23 Sep 2025 09:30:21 +0000
Message-ID: <e88c612071187386f7178a4d519fad7c7f39ab09.camel@groupe-cyllene.com>

>>-------- Message initial --------
>>De: Prashant Patil <Prashant.Gamepatil@arctera.io>
>>À: Proxmox VE development discussion <pve-devel@lists.proxmox.com>
>>Objet: Unable to create persistent dirty-bitmap
>>Date: 23/09/2025 07:23:26

>>Hello,
>>We have configured 'Directory' storage having SAN as backing storage,
>>the SAN storage is mounted at file system path (/mnt/pve/SAN-
>>Storage1) with type ext4. We have couple of VMs running on this
>>storage. When we try to create a persistent bitmap on qcow2 file then
>>that fails with below error. The disk at 'scsi0' is "scsi0: SAN-
>>Storage1:101/vm-101-disk-1.qcow2,iothread=1,size=32G". So, the
>>question here is, why are we getting error to create persistent
>>bitmap for qcow2 disk?
>>
>>root@be1-proxmox1:~# echo '{"execute": "qmp_capabilities"}{"execute":
>>"block-dirty-bitmap-add", "arguments": {"node":"drive-
>>scsi0","name":"bm_1","persistent":true}}' | socat - unix-
>>connect:/var/run/qemu-server/101.qmp
>>{"QMP": {"version": {"qemu": {"micro": 2, "minor": 0, "major": 10},
>>"package": "pve-qemu-kvm_10.0.2-4"}, "capabilities": []}}
>>{"return": {}}
>>{"error": {"class": "GenericError", "desc": "Can't store persistent
>>bitmaps to drive-scsi0: Operation not supported"}}
>>root@be1-proxmox1:~#


I'm not 100% sure, but maybe is it the wrong node ? (on machine model
10, with blockdev enable, we use a throttle node at top node ("drive-
scsi0"),  
maybe it need to be done on the "format" node where qcow2 is available

for example:

 -blockdev '{"driver":"throttle","file":{"cache":{"direct":true,"no-
flush":false},"driver":"qcow2","file":{"aio":"io_uring","cache":{"direc
t":true,"no-flush":false},"detect-
zeroes":"unmap","discard":"unmap","driver":"file","filename":"/var/lib/
vz/images/8006/vm-8006-disk-0.qcow2","node-
name":"edd19f6c1b3a6d5a6248c3376a91a16","read-only":false},"node-
name":"fdd19f6c1b3a6d5a6248c3376a91a16","read-only":false},"node-
name":"drive-virtio0","throttle-group":"throttle-drive-virtio0"}'

you should use the node "fdd19f6c1b3a6d5a6248c3376a91a16"

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