📝 Document storage metrics keys

docs/architecture/database.md

@@ -201,14 +201,25 @@ During the lifecycle of a session each component generates status codes for trac
 }
 ```
 
-#### Slots
+#### Orchestrator
 ```javascript
 `metrics:slots:reclaimed.total` = Hashes {
 	dead = number
 	orphaned = number
 }
 ```
 
+#### Storage
+```javascript
+`metrics:storage:disk.bytes.total` = Hashes {
+	<storage-id> = number
+}
+
+`metrics:storage:disk.bytes.used` = Hashes {
+	<storage-id> = number
+}
+```
+
 ## Garbage collection
 
 Special considerations have been taken to ensure that most keys expire on their own (e.g. active manager/storage/api metadata). Those that do not expire on their own (e.g. sessions) will be purged by a dedicated garbage collector service.