Starting with ocis version 3.0.0, the default backend for metadata switched to messagepack. If the setting STORAGE_SYSTEM_OCIS_METADATA_BACKEND has not been defined manually, the backend will be migrated to messagepack automatically. Though still possible to manually configure xattrs, this setting should not be used anymore as it will be removed in a later version.

Caching

The storage-system service caches file metadata via the configured store in STORAGE_SYSTEM_CACHE_STORE. Possible stores are:

memory: Basic in-memory store and the default.
redis: Stores metadata in a configured Redis cluster.
redis-sentinel: Stores metadata in a configured Redis Sentinel cluster.
etcd: Stores metadata in a configured etcd cluster.
nats-js: Stores metadata using the key-value-store feature of nats jetstream
noop: Stores nothing. Useful for testing. Not recommended in production environments.

Note that in-memory stores are by nature not reboot-persistent.
Though usually not necessary, a database name can be configured for event stores if the event store supports this. Generally not applicable for stores of type in-memory, redis and redis-sentinel. These settings are blank by default which means that the standard settings of the configured store apply.
The storage-system service can be scaled if not using in-memory stores and the stores are configured identically over all instances.
When using redis-sentinel, the Redis master to use is configured via STORAGE_SYSTEM_CACHE_NODES in the form of <sentinel-host>:<sentinel-port>/<redis-master> like 10.10.0.200:26379/mymaster.