Some wording tweaks, clarified PASSIVE mode for cluster shutdown

docs/modules/storage/pages/persistence.adoc

@@ -1,13 +1,13 @@
 = Persisting Data on Disk
-:description: Persistence allows individual members and whole clusters to recover data by persisting map entries, JCache data, and streaming job snapshots on disk. Members can use persisted data to recover from cluster-wide shutdowns and speed up individual member restarts by reducing the volume of data sent over the network.
+:description: Persistence allows individual members and whole clusters to recover data by persisting map entries, JCache data, and streaming job snapshots on disk. Members can use persisted data to recover from planned cluster-wide shutdowns, unplanned cluster-wide failures and speed up individual member restarts by reducing the volume of data sent over the network.
 :toc-levels: 3
 :page-enterprise: true
 
 {description}
 
 == Why Persist Data
 
-Data in Hazelcast is usually stored in-memory (RAM) so that it's faster to access. However, data in RAM is volatile, meaning that when a member shuts down, its data is lost. In-memory partition backups are still the primary method for data resilience in Hazelcast but additionally persisting data to disk can be useful in certain situations. When you persist data on disk, members can load it upon a restart back into memory directly instead of relying on other active members sending it over the network.
+Data in Hazelcast is usually stored in-memory (RAM) so that it's faster to access. However, data in RAM is volatile, meaning that when a member shuts down, its data is lost. In-memory partition backups are the primary method for data resilience in Hazelcast but additionally persisting data to disk can be useful in certain situations. When you persist data on disk, members can load it upon a restart instead of relying on other active members sending it over the network. In the case of cluster-wide failure - e.g. due to data centre power outage - where we cannot rely on receiving the data from other active members, persistence means that we can recover data that would otherwise be irreversibly lost.
 
 Clusters can use persisted data for the following scenarios:
 
@@ -17,7 +17,7 @@ Clusters can use persisted data for the following scenarios:
 +
 [IMPORTANT]
 ====
-In order for persistence to function correctly for planned cluster shutdowns you must xref:maintain-cluster:shutdown.adoc[shutdown the entire cluster at once].
+In order for persistence to function correctly for planned cluster shutdowns you must first put the cluster into `PASSIVE` state before shutting down members. A list of methods for gracefully shutting down a cluster can be found in the xref:maintain-cluster:shutdown.adoc[shutdown] docs.
 ====
 ** **Unplanned**: A cluster is restarted after all its members crash at the same time due an event such as a power outage. Note that some data loss is expected unless `fsync` is set to `true`. For more information, see xref:storage:configuring-persistence.adoc#data-structures[Data structure options].