diff --git a/2025/xg-infra-upgrade-2025.md b/2025/xg-infra-upgrade-2025.md
index f855631..d071060 100644
--- a/2025/xg-infra-upgrade-2025.md
+++ b/2025/xg-infra-upgrade-2025.md
@@ -107,3 +107,5 @@ data/test-dataset/dataset-1   128M   410G   128M  /data/test-dataset/dataset-1
 # External docs
 
 * https://klarasystems.com/articles/openzfs-understanding-zfs-vdev-types/
+* https://jrs-s.net/2018/03/13/zvol-vs-qcow2-with-kvm/
+*