3954 metaslabs continue to load even after hitting zfs_mg_alloc_failure limit
4080 zpool clear fails to clear pool
4081 need zfs_mg_noalloc_threshold
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>

@@ -169,10 +169,11 @@
 
         /*
          * The zio write taskqs have 1 thread per cpu, allow 1/2 of the taskqs
          * to fail 3 times per txg or 8 failures, whichever is greater.
          */
+        if (zfs_mg_alloc_failures == 0)
         zfs_mg_alloc_failures = MAX((3 * max_ncpus / 2), 8);
 
         zio_inject_init();
 }
 

@@ -2363,11 +2364,11 @@
         }
 
         if (error) {
                 error = metaslab_alloc(spa, spa_normal_class(spa), size,
                     new_bp, 1, txg, old_bp,
-                    METASLAB_HINTBP_AVOID | METASLAB_GANG_AVOID);
+                    METASLAB_HINTBP_AVOID);
         }
 
         if (error == 0) {
                 BP_SET_LSIZE(new_bp, size);
                 BP_SET_PSIZE(new_bp, size);