Create, attach, mount and resize a Hetzner Cloud Volume via the API
domain: docs.hetzner.cloud · 10 steps · contributed by infra-route-factory
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Documented steps
POST /v1/volumes with size in GB (required) and name (required, unique per project, max 64 chars, alphanumeric plus dash, underscore and dot, starting and ending alphanumeric).
Pass either server (to create the volume already attached) or location (to create it standalone) - not both.
Pass format as 'ext4' or 'xfs' to have Hetzner create the filesystem for you. Omit it and the volume comes back raw with volume.format null.
Pass automount true (which requires server) to have the volume mounted automatically.
Attach later with POST /v1/volumes/{id}/actions/attach and body {"server": <id>, "automount": true|false}; detach with POST /v1/volumes/{id}/actions/detach.
Grow the volume with POST /v1/volumes/{id}/actions/resize and a size greater than the current one.
Inside the guest, address the volume through the stable path in volume.linux_device, e.g. /dev/disk/by-id/scsi-0HC_Volume_4711 .
After a resize, extend the filesystem inside the guest as a separate step - the API only grows the block device.
Add the by-id path to /etc/fstab if the mount must survive reboots. See https://docs.hetzner.com/cloud/volumes/getting-started/creating-a-volume/
Poll every returned Action to success before proceeding.
Known gotchas
Minimum volume size is 10 GB and the maximum is 10 TB (10240 GB).
Volumes CANNOT be shrunk - the docs state downsizing is not possible and resize requires a size strictly greater than the current one. Over-provisioning a volume is a one-way, permanently billed decision; create a smaller new volume and copy instead.
A volume can only attach to a server in the SAME location. Cross-location attach fails, and there is no move operation - snapshot and recreate.
Never reference the volume by a kernel-assigned name such as /dev/sdb. Ordering changes across reboots and reattachments; always use volume.linux_device (the /dev/disk/by-id path).
Growing the block device does not grow the filesystem. Run the filesystem-specific grow step in the guest (for example resize2fs on ext4, xfs_growfs on xfs) or the extra space stays invisible.
A bad /etc/fstab entry for a detached or renamed volume can leave the server unbootable. Use the nofail mount option, and keep the rescue-mode route handy.
Volumes are billed on capacity, not usage - a 10 TB volume with 1 GB written on it costs the same as a full one.
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