Can external storage systems (e.g. SDS@hd) be used?
Yes, external storage systems can easily be integrated via a network connection. Please be aware that security groups / rules must be configured accordingly.
Can the block storage volumes also be used without an instance or outside of heiCLOUD?
No, the volumes are bound to the platform and must be attached to an instance to be used.
Can data carriers also be downloaded (e.g. for backup purposes) ?
Yes, but only via the CLI. The medium must not be attached to any instance and must first be uploaded as an image. The commands for this are:
openstack image create --volume <volume-name-or-id> <image-name>
glance image-download --file <file name> --progress <image-ID>
Can volumes be shut down so that they do not produce any costs?
No, unfortunately this is not possible. Persistent volumes cause costs as long as they exist.