If you've installed Lion on a drive with too many partitions or an unsupported RAID array, then while the Lion installer will allow you to continue the OS installation, it will just omit setting up the Recovery HD partition. While this partition should be present on most systems running Lion, in some situations it may be missing. When you install OS X Lion, the system will create a hidden partition called 'Recovery HD.' In addition to providing recovery and diagnostics tools similar to those on the older OS X installation DVDs, it is also used for enabling enhanced features in Lion such as Apple's FileVault 2 disk encryption and the 'Find My Mac' location service as part of iCloud.
