Reduce finalization migration frequency

beacon_node/src/cli.rs

@@ -539,6 +539,16 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .takes_value(true)
                 .default_value("true")
         )
+        .arg(
+            Arg::with_name("db-migration-period")
+                .long("db-migration-period")
+                .value_name("EPOCHS")
+                .help("Specifies the number of epochs to wait between applying each finalization \
+                       migration to the database. Applying migrations less frequently can lead to \
+                       less total disk writes.")
+                .default_value("4")
+                .takes_value(true)
+        )
 
         /*
          * Misc.

beacon_node/src/config.rs

@@ -366,6 +366,11 @@ pub fn get_config<E: EthSpec>(
         client_config.store.prune_payloads = prune_payloads;
     }
 
+    if let Some(epochs_per_migration) = clap_utils::parse_optional(cli_args, "db-migration-period")?
+    {
+        client_config.store_migrator.epochs_per_run = epochs_per_migration;
+    }
+
     /*
      * Zero-ports
      *