diff --git a/kubernetes/apps/grafana-db/postgres.yaml b/kubernetes/apps/grafana-db/postgres.yaml
index c4026196..dc2e098e 100644
--- a/kubernetes/apps/grafana-db/postgres.yaml
+++ b/kubernetes/apps/grafana-db/postgres.yaml
@@ -53,6 +53,28 @@ spec:
       # and slower than the lz4/zstd this build also accepts). Compresses the
       # full-page images that dominate WAL volume after each checkpoint.
       wal_compression: "zstd"
+      # THE dominant write source on this cluster, by three orders of magnitude.
+      #
+      # A WAL segment is a fixed 16 MiB file. archive_timeout forces a segment
+      # switch on a timer so the archive never lags reality by more than that
+      # interval -- and the switched-out segment is written and archived at its
+      # full 16 MiB regardless of how few bytes of real WAL it contains.
+      #
+      # CNPG defaults this to 5min, i.e. up to 288 segments/day = 4.6 GB/day.
+      # Measured here: this database is 21 MB and generates 4.5 MB/day of actual
+      # WAL, while its RBD volume takes 211 MB/hour. Essentially every byte
+      # written is padding -- roughly 1100x amplification.
+      #
+      # 30min cuts that to 48 segments/day. The cost is RPO: on total loss of
+      # the cluster, up to 30min of Grafana state is unrecoverable rather than
+      # 5min. Grafana's state here is dashboards, annotations and preferences,
+      # and the write rate says it changes ~4.5 MB/day -- so that window is
+      # nearly always empty anyway.
+      #
+      # Applied to gf-pg FIRST, alone, as a staged rollout: it is the lowest-risk
+      # cluster and has the cleanest signal, since its real WAL is small enough
+      # that any change in volume is unambiguously this parameter.
+      archive_timeout: "30min"
   resources:
     requests:
       cpu: 100m