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How-to

Attach a volume

Attach a volume to an instance as a disk, set it up in the operating system, and detach it when the instance no longer needs it.

An instance can be running or shut down when you attach or detach a volume. A volume is attached to one instance at a time.

Before you start

Attach the volume

  1. In the Breqwatr Cloud Portal (Strata), open Volumes and choose the volume.
  2. Choose Attach to instance.
  3. Pick the Instance and choose Attach.

The Attach to instance dialog on data-volume's page, with web-01 chosen as the instance and an Attach button

The status changes to In-use, and Attached to shows the instance and the device name. The instance's page lists the volume under Volumes.

openstack --os-cloud <cloud-name> server add volume web-01 data-volume

resource "openstack_compute_volume_attach_v2" "data" {
  instance_id = openstack_compute_instance_v2.web_01.id
  volume_id   = openstack_blockstorage_volume_v3.data.id
}

Set it up in the operating system

A new volume is an empty disk: give it a filesystem before you use it. A volume made from a snapshot or a backup already has one, so skip straight to mounting it.

Find the new disk, the one with no partitions or mount point, usually vdb:

lsblk

Make a filesystem on it, and mount it at /mnt/data:

sudo mkfs.ext4 -L data /dev/vdb
sudo mkdir -p /mnt/data
sudo mount /dev/vdb /mnt/data

To mount it at every start, add it to /etc/fstab by its UUID, which doesn't change if the device name does:

sudo blkid -s UUID -o value /dev/vdb
echo "UUID=<uuid> /mnt/data ext4 defaults,nofail 0 2" | sudo tee -a /etc/fstab
sudo systemctl daemon-reload
sudo mount -a

nofail lets the instance start even when the volume isn't attached.

Breqwatr's Windows images leave a newly attached disk offline, and take data disks offline again at each restart. In PowerShell as Administrator, change that once, so disks you bring online stay online:

Set-StorageSetting -NewDiskPolicy OnlineAll

Find the new disk: it's the one that's Offline, usually number 1:

Get-Disk | Format-Table Number, OperationalStatus, PartitionStyle, Size

An empty disk shows the partition style RAW. Bring it online, partition it, give it a drive letter and format it, all in one go:

Get-Disk | Where-Object PartitionStyle -eq RAW | Initialize-Disk -PartitionStyle GPT -PassThru | New-Partition -AssignDriveLetter -UseMaximumSize | Format-Volume -FileSystem NTFS -NewFileSystemLabel data -Confirm:$false

The output shows the new drive, such as D.

A disk that already has a filesystem only needs bringing online, with its number from Get-Disk:

Set-Disk -Number 1 -IsOffline $false

Detach the volume

Stop using the volume in the operating system first: detaching a disk that's still in use can lose data.

  • Linux: sudo umount /mnt/data, and remove its line from /etc/fstab.
  • Windows: close anything using the drive, then take the disk offline, with its number from Get-Disk: Set-Disk -Number 1 -IsOffline $true.

Open the volume and choose Detach. Type CONFIRM and choose Detach. Or, on the instance's page, choose Detach on the volume's row under Volumes.

The boot volume, marked Boot, can't be detached.

openstack --os-cloud <cloud-name> server remove volume web-01 data-volume

Remove the openstack_compute_volume_attach_v2 resource and apply. The volume and its data stay.

The volume goes back to Available, ready to attach to this instance or another one.

Check it worked

  • openstack --os-cloud <cloud-name> volume show data-volume -c status -c attachments shows in-use, the instance's ID and the device name.
  • In the instance, df -h /mnt/data on Linux, or Get-Volume in PowerShell on Windows, shows the new filesystem.