[SOLVED] LXC Backup Error 70: Write Error

[hamborghini_mercy]

I am having an issue when backing up an unprivileged LXC container. The bootdisk size for the LXC is only 16GB, but when I try to back up the LXC (ID 100) it continues indefinitely until it uses all of the space on my "local" storage and then fails. I have no issues backing up my linux VM (ID 101). When the backup fails, I get this error code:

INFO: starting new backup job: vzdump 100 --node proxmox --notes-template '{{cluster}}, {{guestname}}, {{node}}, {{vmid}}' --storage local --mode stop --notification-mode notification-system --compress zstd --remove 0
INFO: Starting Backup of VM 100 (lxc)
INFO: Backup started at 2026-03-11 12:26:40
INFO: status = stopped
INFO: backup mode: stop
INFO: ionice priority: 7
INFO: CT Name: DC1
INFO: including mount point rootfs ('/') in backup
INFO: including mount point mp0 ('/data') in backup
INFO: creating vzdump archive '/var/lib/vz/dump/vzdump-lxc-100-2026_03_11-12_26_40.tar.zst'
INFO: zstd: error 70 : Write error : cannot write block : No space left on device
ERROR: Backup of VM 100 failed - command 'set -o pipefail && lxc-usernsexec -m u:0:100000:65536 -m g:0:100000:65536 -- tar cpf - --totals --one-file-system -p --sparse --numeric-owner --acls --xattrs '--xattrs-include=user.*' '--xattrs-include=security.capability' '--warning=no-file-ignored' '--warning=no-xattr-write' --one-file-system '--warning=no-file-ignored' '--directory=/var/lib/vz/dump/vzdump-lxc-100-2026_03_11-12_26_40.tmp' ./etc/vzdump/pct.conf ./etc/vzdump/pct.fw '--directory=/mnt/vzsnap0' --no-anchored '--exclude=lost+found' --anchored '--exclude=./tmp/?*' '--exclude=./var/tmp/?*' '--exclude=./var/run/?*.pid' ./ ./data | zstd '--threads=1' >/var/lib/vz/dump/vzdump-lxc-100-2026_03_11-12_26_40.tar.dat' failed: exit code 70
INFO: Failed at 2026-03-11 12:43:06
INFO: Backup job finished with errors
INFO: notified via target `mail-to-root`
TASK ERROR: job errors

LXC info:

arch: amd64
cores: 1
features: nesting=1
hostname: DC1
memory: 512
mp0: tank:subvol-100-disk-0,mp=/data,backup=1,replicate=0,size=1000G
net0: name=eth0,bridge=vmbr0,firewall=1,gw=192.168.40.1,hwaddr=BC:24:11:38:D7:98,ip=192.168.40.100/24,type=veth
onboot: 1
ostype: ubuntu
rootfs: local-lvm:vm-100-disk-0,size=16G
swap: 512
unprivileged: 1

Output from lvdisplay:

  --- Logical volume ---
  LV Name                data
  VG Name                pve
  LV UUID                8g8kxB-555s-ALBg-fTnC-2ANd-cB0A-VguWgi
  LV Write Access        read/write (activated read only)
  LV Creation host, time proxmox, 2026-01-22 20:32:46 -0500
  LV Pool metadata       data_tmeta
  LV Pool data           data_tdata
  LV Status              available
  # open                 0
  LV Size                137.11 GiB
  Allocated pool data    50.27%
  Allocated metadata     2.59%
  Current LE             35101
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:5
  
  --- Logical volume ---
  LV Path                /dev/pve/swap
  LV Name                swap
  VG Name                pve
  LV UUID                DUYNZ3-xwfO-HEcQ-juyE-dy0o-OcSg-5c82f6
  LV Write Access        read/write
  LV Creation host, time proxmox, 2026-01-22 20:32:46 -0500
  LV Status              available
  # open                 1
  LV Size                8.00 GiB
  Current LE             2048
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:0
  
  --- Logical volume ---
  LV Path                /dev/pve/root
  LV Name                root
  VG Name                pve
  LV UUID                sEpfg6-FVQe-zQQH-gpd8-PDRS-LiD6-0sSUaI
  LV Write Access        read/write
  LV Creation host, time proxmox, 2026-01-22 20:32:46 -0500
  LV Status              available
  # open                 1
  LV Size                80.00 GiB
  Current LE             20480
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:1
  
  --- Logical volume ---
  LV Path                /dev/pve/vm-101-disk-0
  LV Name                vm-101-disk-0
  VG Name                pve
  LV UUID                LTwq6T-byMd-Q0XG-iJxL-zvwC-HZxc-bU3L0N
  LV Write Access        read/write
  LV Creation host, time proxmox, 2026-02-16 19:19:04 -0500
  LV Pool name           data
  LV Status              available
  # open                 0
  LV Size                80.00 GiB
  Mapped size            81.49%
  Current LE             20480
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:6
  
  --- Logical volume ---
  LV Path                /dev/pve/vm-100-disk-0
  LV Name                vm-100-disk-0
  VG Name                pve
  LV UUID                jNcV8Z-7CfB-xZU8-m2xW-trG0-12y4-FNOduz
  LV Write Access        read/write
  LV Creation host, time proxmox, 2026-03-05 20:00:34 -0500
  LV Pool name           data
  LV Status              available
  # open                 0
  LV Size                16.00 GiB
  Mapped size            23.39%
  Current LE             4096
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:7

 

[Impact]

What's df -hT look like? Your CT's disk is 1000G and your destination is only 80G. I'm not sure how much data the CT uses (share df -hT inside of it and lvs) but local is not a good target for storing the backup.

 

[hamborghini_mercy]

What's df -hT look like? Your CT's disk is 1000G and your destination is only 80G. I'm not sure how much data the CT uses (share df -hT inside of it and lvs) but local is not a good target for storing the backup.

Thank you for pointing that out. I only wanted to back up the bootdisk (16GB), not the 1TB mount HDD. All I had to do was click on the LXC -> Resources -> Mount Point -> Edit button on ribbon -> Uncheck Backup.