Horde Storage Configuration

Introduction

Many features use Horde's storage system within the server. In many respects, the storage layer functions as an immutable content-addressable store (i.e. items are stored and retrieved via a hash of their content), though the on-disk representation consists of data packed into larger bundles stored with unique identifiers in a more familiar location-based storage backend.

An important feature of this system is the ability to reason about massive data structures; that is, individual nodes in the storage system (some arbitrary block of data) are characterized by being immutable and having zero or more outward references to other nodes. These tree-like data structures can be traversed one node at a time, with the underlying storage system retrieving and storing individual nodes efficiently.

The entry point to any such data structure is a ref, a user-defined name that keeps a reference to the root of the tree. Any nodes not directly or indirectly referenced by a ref are subject to garbage collection.

This design intends to support a massive range of payload sizes by splitting larger data blocks into smaller chunks and has advantages in caching and incremental client data patching. With this, it becomes reasonable to have a ref point to a single 4kb payload as it is to point to a multi-gigabyte payload split into 128kb chunks.

Namespaces and Backends

Storage is partitioned into several non-overlapping namespaces, each of which can be configured to use a different backend. Permissions to access content in storage is normally controlled at the namespace level, though some higher-level systems (e.g. logs, artifacts) expose custom endpoints over underlying storage namespaces which provide their own permissions model that does not require direct access to the backing namespace.

Namespaces and backends are configured through the Storage section of the globals.json file.

Namespaces

Namespaces configure permissions and garbage collection policies for a logical storage partition. They also specify a backend to use for storing the actual data.

Multiple namespaces may use the same storage backend by setting the Prefix property to append a prefix to any stored files.

Settings for namespaces are described in the globals.json schema.

Backends

Horde supports several storage backends, as well as local on-disk and in-memory caches:

• Local disk
• Network shares
• AWS S3 Object Store
• Azure Blob Store

Settings for backends are described in the globals.json schema.

Well-known Namespaces

Certain subsystems in Horde use well-known namespace names, which can be configured as you see fit. These are defined in StorageConfig.cs and currently consist of the following:

References

• Glossary