More details on and system-design implications of the Hitachi-LG Data Storage HyDrive Optical/Solid-State Disk

As discussed last week in this blog, Hitachi-LG Data Storage (HLDS)--an OEM vendor of optical drives that’s a joint venture between Hitachi and LG--introduced a combo optical/solid-state drive called HyDrive last week at Computex 2010 in Taipei with a few more technical details about the drive. (See: How does a hybrid SSD/optical drive make sense?) The initial version of the HyDrive will reportedly be based on a DVD burner/Blu-ray disc player with 32 or 64 Gbytes of NAND Flash configured as an SSD. One 3-Gbps SATA II interface accesses both the optical and solid-state drives in the first-generation HyDrive. The internal SSD controller is enhanced with “Defect Management technology” that allows the SSD to buffer the data streaming from the optical disk to smooth the gaps and jumps in the playback stream caused by lapses in the stream due to scratched optical media as demonstrated by the video clips discussed in the previous blog entry.

The HLDS press release says that the HyDrive’s on-board controller can boost a host PC’s performance in one of two ways:

1. The entire on-board SSD can operate as a cache using a Windows filter driver supplied by HLDS.
2. Part of the on-board SSD can be used to image the Windows operating system and applications, speeding boot and application-loading times by 30 to 60%. Whatever remains of the SSD capacity is used as a cache.

The first-generation HyDrive is thick--12.7mm--so it doesn’t fit into existing laptop slots for optical drives. However, HLDS says that first-generation HyDrives will ship in the MN 102-O Family PC from entertainment-PC vendor Moneual Lab in August with general availability scheduled for September. HLDS also announced plans to reduce the thickness of second-generation HyDrives to 9.5 mm, making many more optical-drive slots available for the storage product. The second-generation HyDrive is also expected to have a maximum SSD capacity of 256 Gbytes, will offer a faster SATA III 6-Gbps interface, and is expect to debut in March, 2011.

System designers may want to think carefully about the architectural implications of the HyDrive approach, which multiplexes one SATA interface between the SSD and the optical drive. The SATA II interface has ample bit capacity for playing Blu-ray video, which requires less than 50 Mbps. However, LG already offers a 10x Blu-ray drive, so the optical drive section of the HyDrive might consume a substantial portion of the first-generation HyDrive’s SATA II interface. Any portion of the SATA interface’s bandwidth consumed by the optical drive is not available for the SSD when both drives are operating and, of course, there’s always overhead to deal with when multiplexing one interface to two drives, which will play a factor in the ultimate performance of the HyDrive approach even with the second-generation’s faster SATA III interface.

There’s also the physical form factor of the optical drive to consider. The inability to stuff the SSD into a laptop-compatible optical drive’s physical envelope in this first-generation HyDrive shows that integrating an SSD into an optical drive isn’t as simple as adding a circuit board to an existing product. Tighter and more pervasive integration is required. Yet there will still be compromises when that closer integration takes place because the SSD can only be allocated so much volume within the drive’s envelope. Some of the optical drive’s components including the disc bay, drive motor, and head/actuator mechanism have irreducible volumes (or nearly so). As a result, the SSD’s data capacity will be severely limited by the volume made available to it within the HyDrive.

The HyDrive concept makes life theoretically easier for PC and laptop vendors by creating a plug-and-play way to install an SSD into a PC or laptop. However, bundling an optical drive with an SSD in one physical envelope that was previously reserved and optimized for the optical drive alone entails its own set of engineering compromises with respect to data capacity and transfer rate. Contrast this approach with one that places a tailored SSD or Flash cache somewhere else within the PC or laptop. Doing so allows the SSD to use unusually shaped volumes within the mechanical design of the laptop or PC and to have undivided use of much faster interfaces, such as the PCIe interface that’s become abundant in chipset designs. An unbundled approach to NAND Flash caching within a PC or laptop allows system designers to make their own product-specific compromises to better deliver the SSD’s value in terms of speed, performance, and capacity, which in turn commands more revenue from the consumer.