diff --git a/openstack/db/v1/configurations/requests.go b/openstack/db/v1/configurations/requests.go
index 035ff29..abb0013 100644
--- a/openstack/db/v1/configurations/requests.go
+++ b/openstack/db/v1/configurations/requests.go
@@ -1,8 +1,6 @@
 package configurations
 
 import (
-	"errors"
-
 	"github.com/gophercloud/gophercloud"
 	"github.com/gophercloud/gophercloud/openstack/db/v1/instances"
 	"github.com/gophercloud/gophercloud/pagination"
@@ -67,10 +65,16 @@
 // ToConfigCreateMap casts a CreateOpts struct into a JSON map.
 func (opts CreateOpts) ToConfigCreateMap() (map[string]interface{}, error) {
 	if opts.Name == "" {
-		return nil, errors.New("Name is a required field")
+		err := gophercloud.ErrMissingInput{}
+		err.Function = "configurations.ToConfigCreateMap"
+		err.Argument = "configurations.CreateOpts.Name"
+		return nil, err
 	}
 	if len(opts.Values) == 0 {
-		return nil, errors.New("Values must be a populated map")
+		err := gophercloud.ErrMissingInput{}
+		err.Function = "configurations.ToConfigCreateMap"
+		err.Argument = "configurations.CreateOpts.Values"
+		return nil, err
 	}
 
 	config := map[string]interface{}{
diff --git a/openstack/db/v1/databases/requests.go b/openstack/db/v1/databases/requests.go
index ff57245..18e1af5 100644
--- a/openstack/db/v1/databases/requests.go
+++ b/openstack/db/v1/databases/requests.go
@@ -1,8 +1,6 @@
 package databases
 
 import (
-	"fmt"
-
 	"github.com/gophercloud/gophercloud"
 	"github.com/gophercloud/gophercloud/pagination"
 )
@@ -12,7 +10,7 @@
 	ToDBCreateMap() (map[string]interface{}, error)
 }
 
-// DatabaseOpts is the struct responsible for configuring a database; often in
+// CreateOpts is the struct responsible for configuring a database; often in
 // the context of an instance.
 type CreateOpts struct {
 	// [REQUIRED] Specifies the name of the database. Valid names can be composed
@@ -39,10 +37,17 @@
 // into sub-maps.
 func (opts CreateOpts) ToMap() (map[string]string, error) {
 	if opts.Name == "" {
-		return nil, fmt.Errorf("Name is a required field")
+		err := gophercloud.ErrMissingInput{}
+		err.Function = "databases.ToMap"
+		err.Argument = "databases.CreateOpts.Name"
 	}
 	if len(opts.Name) > 64 {
-		return nil, fmt.Errorf("Name must be less than 64 chars long")
+		err := gophercloud.ErrInvalidInput{}
+		err.Function = "databases.ToMap"
+		err.Argument = "databases.CreateOpts.Name"
+		err.Value = opts.Name
+		err.Info = "Must be less than 64 chars long"
+		return nil, err
 	}
 
 	db := map[string]string{"name": opts.Name}
diff --git a/openstack/db/v1/instances/requests.go b/openstack/db/v1/instances/requests.go
index 7714a21..8e33dfe 100644
--- a/openstack/db/v1/instances/requests.go
+++ b/openstack/db/v1/instances/requests.go
@@ -1,8 +1,6 @@
 package instances
 
 import (
-	"fmt"
-
 	"github.com/gophercloud/gophercloud"
 	db "github.com/gophercloud/gophercloud/openstack/db/v1/databases"
 	"github.com/gophercloud/gophercloud/openstack/db/v1/users"
@@ -20,6 +18,7 @@
 	Type    string
 }
 
+// ToMap converts a DatastoreOpts to a map[string]string (for a request body)
 func (opts DatastoreOpts) ToMap() (map[string]string, error) {
 	return map[string]string{
 		"version": opts.Version,
@@ -55,10 +54,18 @@
 // ToInstanceCreateMap will render a JSON map.
 func (opts CreateOpts) ToInstanceCreateMap() (map[string]interface{}, error) {
 	if opts.Size > 300 || opts.Size < 1 {
-		return nil, fmt.Errorf("Size (GB) must be between 1-300")
+		err := gophercloud.ErrInvalidInput{}
+		err.Function = "instances.ToInstanceCreateMap"
+		err.Argument = "instances.CreateOpts.Size"
+		err.Value = opts.Size
+		err.Info = "Size (GB) must be between 1-300"
+		return nil, err
 	}
 	if opts.FlavorRef == "" {
-		return nil, fmt.Errorf("FlavorRef is a required field")
+		err := gophercloud.ErrMissingInput{}
+		err.Function = "instances.ToInstanceCreateMap"
+		err.Argument = "instances.CreateOpts.FlavorRef"
+		return nil, err
 	}
 
 	instance := map[string]interface{}{
@@ -83,6 +90,13 @@
 		}
 		instance["users"] = users["users"]
 	}
+	if opts.Datastore != nil {
+		datastore, err := opts.Datastore.ToMap()
+		if err != nil {
+			return nil, err
+		}
+		instance["datastore"] = datastore
+	}
 
 	return map[string]interface{}{"instance": instance}, nil
 }
diff --git a/openstack/db/v1/users/requests.go b/openstack/db/v1/users/requests.go
index 8f86297..6815c1c 100644
--- a/openstack/db/v1/users/requests.go
+++ b/openstack/db/v1/users/requests.go
@@ -1,8 +1,6 @@
 package users
 
 import (
-	"errors"
-
 	"github.com/gophercloud/gophercloud"
 	db "github.com/gophercloud/gophercloud/openstack/db/v1/databases"
 	"github.com/gophercloud/gophercloud/pagination"
@@ -42,13 +40,24 @@
 func (opts CreateOpts) ToMap() (map[string]interface{}, error) {
 
 	if opts.Name == "root" {
-		return nil, errors.New("root is a reserved user name and cannot be used")
+		err := gophercloud.ErrInvalidInput{}
+		err.Function = "users.ToUserCreateMap"
+		err.Argument = "users.CreateOpts.Name"
+		err.Value = "root"
+		err.Info = "root is a reserved user name and cannot be used"
+		return nil, err
 	}
 	if opts.Name == "" {
-		return nil, errors.New("Name is a required field")
+		err := gophercloud.ErrMissingInput{}
+		err.Function = "users.ToUserCreateMap"
+		err.Argument = "users.CreateOpts.Name"
+		return nil, err
 	}
 	if opts.Password == "" {
-		return nil, errors.New("Password is a required field")
+		err := gophercloud.ErrMissingInput{}
+		err.Function = "users.ToUserCreateMap"
+		err.Argument = "users.CreateOpts.Password"
+		return nil, err
 	}
 
 	user := map[string]interface{}{