[SOLVED] Proxmox Backup Fails – NFS Storage Turns Read-Only During Job

[semihtest]

Hi everyone,

I’m running into issues with my Proxmox backup jobs and could use some advice.

Setup:

• Proxmox VE 7.2-3
• Backups go to an NFS share on a NAS (mounted as /mnt/pve/EXAMPLENAS001)
• Using vzdump with snapshot mode and zstd compression

Problem:
The backup job starts fine. VM 101 completes successfully, but when it moves on to VM 102, the process fails with the following errors:

zstd: error 25 : Write error : Input/output error (cannot write compressed block)
Warning: unable to close filehandle properly: Read-only file system
ERROR: vma_queue_write: write error - Broken pipe
INFO: aborting backup job
ERROR: Backup of VM 102 failed - vma_queue_write: write error - Broken pipe
cp: cannot create regular file '/mnt/pve/EXAMPLENAS001/dump/vzdump-qemu-102-2025_09_10-14_24_35.log': Read-only file system
ERROR: Backup of VM 103 failed - unable to create temporary directory '/mnt/pve/EXAMPLENAS001/dump/vzdump-qemu-103-2025_09_10-15_11_03.tmp'

Entire Log:

Proxmox
Virtual Environment 7.2-3
Search
Node 'EXAMPLEPROXMOX001'
Server View
Logs
INFO: starting new backup job: vzdump 102 101 103 --prune-backups 'keep-last=7' --storage EXAMPLENAS001 --quiet 1 --mode snapshot --mailto [EMAIL]helpdesk@example.com[/EMAIL] --mailnotification failure --notes-template '{{guestname}}' --compress zstd
INFO: Starting Backup of VM 101 (qemu)
INFO: Backup started at 2025-09-10 13:50:00
INFO: status = running
INFO: VM Name: EXAMPLEVM001
INFO: include disk 'scsi0' 'local-lvm:vm-101-disk-0' 80G
INFO: include disk 'scsi1' 'local-lvm:vm-101-disk-1' 300G
INFO: include disk 'scsi2' 'local-lvm:vm-101-disk-2' 310G
INFO: backup mode: snapshot
INFO: ionice priority: 7
INFO: snapshots found (not included into backup)
INFO: creating vzdump archive '/mnt/pve/EXAMPLENAS001/dump/vzdump-qemu-101-2025_09_10-13_50_00.vma.zst'
INFO: started backup task '36422014-3c91-44cd-aa21-6b7800dfbe4e'
INFO: resuming VM again
...
INFO: removing backup 'EXAMPLENAS001:backup/vzdump-qemu-101-2025_09_03-13_50_00.vma.zst'
INFO: pruned 1 backup(s) not covered by keep-retention policy
INFO: Finished Backup of VM 101 (00:34:35)
INFO: Backup finished at 2025-09-10 14:24:35
INFO: Starting Backup of VM 102 (qemu)
INFO: Backup started at 2025-09-10 14:24:35
INFO: status = running
INFO: VM Name: EXAMPLEVM002
INFO: include disk 'scsi0' 'local-lvm:vm-102-disk-0' 160G
INFO: include disk 'scsi1' 'local-lvm:vm-102-disk-1' 100G
INFO: include disk 'scsi2' 'local-lvm:vm-102-disk-2' 300G
INFO: backup mode: snapshot
INFO: ionice priority: 7
INFO: snapshots found (not included into backup)
INFO: creating vzdump archive '/mnt/pve/EXAMPLENAS001/dump/vzdump-qemu-102-2025_09_10-14_24_35.vma.zst'
INFO: started backup task '718e9fa6-10f9-4f0e-975e-136b648add9a'
INFO: resuming VM again
...
zstd: error 25 : Write error : Input/output error (cannot write compressed block)
Warning: unable to close filehandle GEN8420 properly: Read-only file system at /usr/share/perl5/PVE/VZDump/QemuServer.pm line 764.
ERROR: vma_queue_write: write error - Broken pipe
INFO: aborting backup job
INFO: resuming VM again
ERROR: Backup of VM 102 failed - vma_queue_write: write error - Broken pipe
INFO: Failed at 2025-09-10 15:11:03
cp: cannot create regular file '/mnt/pve/EXAMPLENAS001/dump/vzdump-qemu-102-2025_09_10-14_24_35.log': Read-only file system
ERROR: Backup of VM 103 failed - unable to create temporary directory '/mnt/pve/EXAMPLENAS001/dump/vzdump-qemu-103-2025_09_10-15_11_03.tmp' at /usr/share/perl5/PVE/VZDump.pm line 889.
INFO: Failed at 2025-09-10 15:11:03
INFO: Backup job finished with errors
TASK ERROR: job errors

So basically:

• First VM backup works.
• During the second VM, the target storage suddenly becomes read-only.
• After that, all following backups fail.

What I’ve checked so far:

• NAS itself looks fine (no obvious disk errors reported).
• Network between Proxmox and NAS seems stable.

We didn't always have this problem; the backups used to run smoothly and nothing was changed. Has anyone else observed this behaviour? Could it be an NFS problem, a problem with the NAS hard drive, or something in Proxmox that causes the share to switch to read-only mode? Any tips on which protocols or tests I should focus on would be very helpful.


Thanks in advance!

 

[Kingneutron]

Do you have at least 691GB free on the destination storage?

 

[semihtest]

Hello,

Yes, I still have 1.18 TB free in the NAS, so that shouldn't be a problem.

 

[gfngfn256]

Proxmox VE 7.2-3

You probably should update to newer version, Proxmox VE 7 has been EOL since 2024-07.

Yes, I still have 1.18 TB free in the NAS, so that shouldn't be a problem.

Not sure if that is enough.

Your first backup of VM 101 (successful) created (up to) 690G & then pruned 1 backup, this pruning may take time on your NAS end, then the next backup VM 102 attempts to create a backup of 560G - so this could be a total of 690+690+560 = 1940G!

Even without the older backups (prune) - you are still pretty limited as the creation of the backup is also going to use tmp space while creating.

To test: free up space (1tb?) on that NAS & test again.

 

[semihtest]

You probably should update to newer version, Proxmox VE 7 has been EOL since 2024-07.


Not sure if that is enough.

Your first backup of VM 101 (successful) created (up to) 690G & then pruned 1 backup, this pruning may take time on your NAS end, then the next backup VM 102 attempts to create a backup of 560G - so this could be a total of 690+690+560 = 1940G!

Even without the older backups (prune) - you are still pretty limited as the creation of the backup is also going to use tmp space while creating.

To test: free up space (1tb?) on that NAS & test again.

Thank you very much for your support! I have completely emptied the NAS -> the backups are now working perfectly!!!

 

[gfngfn256]

Thank you very much for your support! I have completely emptied the NAS -> the backups are now working perfectly!!!

Good!

Happy you got it sorted, maybe mark this thread as Solved. At the top of the thread, choose the Edit thread button, then from the (no prefix) dropdown choose Solved.