diff --git a/docs/modules/fault-tolerance/pages/backups.adoc b/docs/modules/fault-tolerance/pages/backups.adoc index e693f20ba..e475afb06 100644 --- a/docs/modules/fault-tolerance/pages/backups.adoc +++ b/docs/modules/fault-tolerance/pages/backups.adoc @@ -7,6 +7,15 @@ The distribution happens on the partition level; the data and its backups are st memory partitions. See the xref:overview:data-partitioning.adoc[Data Partitioning] and xref:clusters:partition-group-configuration.adoc[Partition Grouping] for more information about the partitioning. +[IMPORTANT] +==== +Hazelcast does not support backup redistribution on a data structure level. Thus, changing the backup count of a nonempty data structure is **not** supported. For example, for a map: + +1. increasing the backup countfootnote:change-backup-count[The backup count of an empty map can only be changed by modifying the xref:configuration:understanding-configuration.adoc#static-configuration[static configuration] and restarting the cluster.] does **not** create additional copies of existing map entries, +2. decreasing the backup countfootnote:change-backup-count[] does **not** remove any backups of existing map entries, so some backups will have stale data if the map entries are overwritten, and +3. if some backups are lost due to node failure, additional copies are **not** created on other nodes to meet the backup count. +==== + When a member in your cluster is lost, Hazelcast redistributes the backups on the remaining members so that every partition has a backup. The number of backups is configurable.