docs: add details for backups
diff --git a/roles/percona_xtradb_cluster/README.md b/roles/percona_xtradb_cluster/README.md
index cb07653..d41f7e8 100644
--- a/roles/percona_xtradb_cluster/README.md
+++ b/roles/percona_xtradb_cluster/README.md
@@ -13,9 +13,17 @@
## Local storage
The following example shows a backup that runs daily at 6AM to a persistent
-volume with 3 backups kept. The size of the persistent volume is 500Gi in the
+volume with 3 backups kept. The size of the persistent volume is 50Gi in the
example below.
+> **Note**
+>
+> The Percona Operator for MySQL creates a persistent volume claim for every
+> single backup. This means that if you have 3 backups kept, you will have 3
+> persistent volume claims. It's best to set the storage in that case to the
+> size of a single backup (or perhaps match your backup size to the size of the
+> cluster storage, which defaults to `160Gi`).
+
```yaml
percona_xtradb_cluster_spec:
backup:
@@ -29,7 +37,7 @@
- ReadWriteOnce
resources:
requests:
- storage: 500Gi
+ storage: 50Gi
schedule:
- name: daily
schedule: 0 6 * * *