Revert "Update main.yml"

Related to #646

This reverts commit d1c93aa8befd6b6ecc24bc11755854212663c732.
diff --git a/roles/loki/vars/main.yml b/roles/loki/vars/main.yml
index 70f6906..f00b0ab 100644
--- a/roles/loki/vars/main.yml
+++ b/roles/loki/vars/main.yml
@@ -37,7 +37,7 @@
     nodeSelector:
       openstack-control-plane: enabled
     persistence:
-      size: 512Gi
+      size: 256Gi
   gateway:
     image:
       registry: "{{ atmosphere_images['loki_gateway'] | vexxhost.kubernetes.docker_image('domain') }}"