Unmounting a volume means making its filesystem inaccessible to the operating system, so it can’t be actively written to or read from. To protect data integrity, it’s best to unmount a volume before resizing or detaching it.
To unmount a volume, you need to know its mount point, which you can find with
sudo df --human-readable --print-type
The volume mount point will look something like
Filesystem Type Size Used Avail Use% Mounted on . . . /dev/sda ext4 99G 60M 94G 1% /mnt/volume-sfo2-01 . . .
umount to unmount the volume, making sure to substitute in its mount point.
sudo umount --verbose /mnt/mount_point
If the volume is busy, you’ll see output like this:
umount: /mnt/mount_point: target is busy (In some cases useful info about processes that use the device is found by lsof(8) or fuser(1).)
You can see if any processes are currently using the mounted filesystem by passing the mount point to
cd ~ sudo lsof +f -- /mnt/mount_point
If the command displays any output, you will have to stop the listed processes before unmounting the filesystem.
If the volume is safe to unmount,
umount will return:
umount: /mnt/mount_point unmounted
If you will not be reattaching the volume, adjust the
/etc/fstab file to remove any entries referencing the volume:
sudo nano /etc/fstab
You may also wish to remove the mount point if you will not be using it again:
sudo rmdir /mnt/mount_point
Once the volume is unmounted, you can safely proceed to resize or detach it.