diff --git a/doc/rapi.rst b/doc/rapi.rst
index 313364cae3b0890b687ea481dc3c9180efc5028a..17dc56029cb4003c275a62db912cd23263494cce 100644
--- a/doc/rapi.rst
+++ b/doc/rapi.rst
@@ -185,7 +185,8 @@ The instance policy specification is a dict with the following fields:
                                      constants.ISPECS_MAX,
                                      constants.ISPECS_STD,
                                      constants.IPOLICY_DTS,
-                                     constants.IPOLICY_VCPU_RATIO])
+                                     constants.IPOLICY_VCPU_RATIO,
+                                     constants.IPOLICY_SPINDLE_RATIO])
 
 
 .. pyassert::
@@ -220,6 +221,8 @@ The instance policy specification is a dict with the following fields:
   A `list` of disk templates allowed for instances using this policy
 :pyeval:`constants.IPOLICY_VCPU_RATIO`
   Maximum ratio of virtual to physical CPUs (`float`)
+:pyeval:`constants.IPOLICY_SPINDLE_RATIO`
+  Maximum ratio of instances to their node's ``spindle_count`` (`float`)
 
 Usage examples
 --------------
diff --git a/lib/constants.py b/lib/constants.py
index f88233edb984ca5ebf68fead0a956d834a6b0fd6..2fd54327212d74fb1d5c8e2a2b27265eadfb636f 100644
--- a/lib/constants.py
+++ b/lib/constants.py
@@ -956,6 +956,7 @@ ISPECS_MAX = "max"
 ISPECS_STD = "std"
 IPOLICY_DTS = "disk-templates"
 IPOLICY_VCPU_RATIO = "vcpu-ratio"
+IPOLICY_SPINDLE_RATIO = "spindle-ratio"
 
 IPOLICY_ISPECS = frozenset([
   ISPECS_MIN,
@@ -965,6 +966,7 @@ IPOLICY_ISPECS = frozenset([
 
 IPOLICY_PARAMETERS = frozenset([
   IPOLICY_VCPU_RATIO,
+  IPOLICY_SPINDLE_RATIO,
   ])
 
 IPOLICY_ALL_KEYS = (IPOLICY_ISPECS |
@@ -1900,6 +1902,8 @@ NICC_DEFAULTS = {
   NIC_LINK: DEFAULT_BRIDGE,
   }
 
+# All of the following values are quite arbitrarily - there are no
+# "good" defaults, these must be customised per-site
 IPOLICY_DEFAULTS = {
   ISPECS_MIN: {
     ISPEC_MEM_SIZE: 128,
@@ -1924,6 +1928,7 @@ IPOLICY_DEFAULTS = {
     },
   IPOLICY_DTS: DISK_TEMPLATES,
   IPOLICY_VCPU_RATIO: 4.0,
+  IPOLICY_SPINDLE_RATIO: 32.0,
   }
 
 MASTER_POOL_SIZE_DEFAULT = 10