To be able to build both PV and HVM images, it is not possible to use both /dev/sd[f-p] and [1-16] as the HVM images get attached at /dev/sdf but must be mounted a /dev/sdf1.

This reduces the number of simultaneous packer runs possible significantly, but unless you are Netflix, who have Aminator anyway, this is probably never going to be an issue

builder/amazon/chroot/device.go

@@ -27,11 +27,12 @@ func AvailableDevice() (string, error) {
 			continue
 		}
 
-		for i := 1; i < 16; i++ {
-			device := fmt.Sprintf("/dev/%s%c%d", prefix, letter, i)
-			if _, err := os.Stat(device); err != nil {
-				return device, nil
-			}
+		// To be able to build both Paravirtual and HVM images, the unnumbered
+		// device and the first numbered one must be available. 
+		// E.g. /dev/xvdf  and  /dev/xvdf1
+		numbered_device := fmt.Sprintf("%s%d", device, 1)
+		if _, err := os.Stat(numbered_device); err != nil {
+			return device, nil
 		}
 	}