HTTP_mirror_pool.md

@@ -53,6 +53,10 @@ Maintaining the pool is:
   is not resilient to broken mirrors" and "there's often a broken mirror",
   any breakage impacts UX negatively
 
+Additionally, slow mirrors make our monitoring take vastly longer than it could.
+This makes it difficult for sysadmins to schedule properly (sysadmin#17702),
+and reports error later than it could.
+
 ## The plan
 
 ### Make our software more resilient to broken mirrors