Alternative proposal for a volume type standard

Signed-off-by: Matthias Büchse <[email protected]>

Standards/scs-0112-v1-volume-types.md

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+---
+title: SCS Volume Types
+type: Standard
+status: Draft
+track: IaaS
+---
+
+
+## Introduction
+
+A volume is a virtual drive that is to be used by an instance (i. e., a virtual machine). With OpenStack,
+each volume is created per a type that determines basic features of the volume as provided by the backend,
+such as encryption, replication, or quality of service. As of the writing of this document, none of these
+features can be discovered by non-privileged users via the OpenStack API.
+
+## Motivation
+
+As an SCS user, I want to be able to create volumes with certain common features, such as encryption or
+replication, and to do so in a standardized manner as well as programmatically.
+This standard outlines a way of formally advertising these common features for a volume type to
+non-privileged users, so that the most suitable volume type can be discovered and selected easily--both by
+the human user and by a program.
+
+## Possible features
+
+The following features are recognized.
+
+| name  | meaning  |
+| :--    | :--  |
+| `encrypted`  | volumes of this type are encrypted  |
+| `replicated` | volumes of this type are replicated (at least threefold)  |
+
+Further features may be added in the future, as outlined in detail in the [decision record regarding volume
+types.](https://github.com/SovereignCloudStack/standards/blob/main/Standards/scs-0111-v1-volume-type-decisions.md)
+
+## Advertising features
+
+The features of a volume type MAY be advertised by putting a _feature list_ in front of its description.
+A feature list has the following form:
+
+`[feat:`feat1,feat2,...,featN`]`
+
+where the entries (feat1, ..., featN) are sorted alphabetically, and each entry occurs at most once.
+
+## Recommended volume types
+
+At least one volume type SHOULD feature encryption.
+
+At least one volume type SHOULD feature replicaton.
+
+Note that the two preceding conditions can be satisfied by a single volume type if it has both features.
+In this case, the description of this volume type would start as follows:
+
+`[feat:encrypted,replicated]`
+
+## Related Documents
+
+- corresponding [decision record document](https://github.com/SovereignCloudStack/standards/blob/main/Standards/scs-0111-v1-volume-type-decisions.md)
+
+## Conformance Tests
+
+TO DO: the test script shall test the following:
+
+- for each volume type: if its description starts with `[feat:....]`, then this prefix is a feature list
+  (sorted, each entry at most once), and each entry is one of the possible features described here;
+  otherwise, an ERROR is produced
+- the recommended volume types are present (otherwise, a WARNING is produced)