Solid State Hard Disk Drives

Solid State Hard Disk Drives (SSD), or at least the idea of them is taking the industry by storm. Like many new technologies, expectations are high, but on the hype vs. delivery continuum, the technology is currently leaning much more toward people saying that they've heard 200% performance increases and 8000% reliability improvement over traditional hard disk drive (HDD) technology. (Personally, what I've heard is that if Ferris dies he's giving his eyes to Stevie Wonder.) For those that may not be familiar with the technology, traditional hard disk drives that are the standard for data storage today have some limitations. They are the single biggest performance bottleneck in a system. They are also relatively fragile. SSD is used in place of a traditional HDD. It replaces the spinning platters with solid state "flash" memory. The promises are much improved reliability and performance. Lenovo does not currently offer solid state HDDs as options on our products, but customer demand is increasing. We want to be sure that what we offer will meet customer expectations. I wanted to look at some of the technical aspects of the technology and a bit about the state of the industry as it pertains to us for incorporation into our products. Before we begin, I am indebted to Don Frame and Jeff Hobbet here at Lenovo for providing much of the technical content. Thank you. There are four axes to examine with regards to SSDs: performance, reliability, power consumption and cost. As with any technology, there are tradeoffs, especially with the first generation of drives available now.

Performance Today's' drives offer very fast random access and read transfer rates compared to hard disk drives. On the other hand, they have very slow write performance. Programming and erasure account for much of this. Performance numbers are inconsistent and very dependent on factors like percentage of space used and file fragmentation. Plus, performance tends to degrade over time. This is definitely a time when the choice of benchmark will affect results. Those benchmarks with sequential reads or writes will have markedly different results than those testing with random reads and writes. Internally, our team has benchmarked performance to be anywhere from 3X the performance of a hard drive to less than a standard hard drive. Proceed with caution when someone throws numbers at you. For future generations, Lenovo is working with suppliers to implement write buffering techniques and algorithms to minimize performance lag.

Reliability There is no question that solid state drives are much more robust than a standard hard drive. They have approximately 6X the shock resistance and a 20% improvement in temperature range. On the other hand, while the drives are more robust, the underlying technology still has limitations. Inside the drive the NAND technology has a 100,000 erase cycle lifetime for a single level cell or 10,000 erase cycle lifetime for a multi-level cell. Multi-level cells are used to increase capacity. User and operating system scenarios exceed program lifecycles of the technology. Things like swap file usage or even a user defragmenting a disk add write cycles which can cause premature wear. This can be mitigated by wear-leveling algorithms which spread out usage across the memory cells, but this is still technology in its infancy. Lenovo's engineering teams have been working with suppliers to ensure that there are not data integrity or corruption problems. This is a partnership to help SSD suppliers mature their technology and improve erase cycle limitations. In addition, it is likely customers will require encryption options to secure their data. Our engineers are working on that too.

Power Consumption Solid state HDDs promise to save power compared to traditional hard disk technology. And they will. However today's generation of SSDs have no power savings benefit compared to traditional HDDs. The big reason is that current SSDs with a Serial ATA interface are actually Parallel ATA hard disk drives with a serial bridge chip. They don't offer support for low power interface states and the architecture has a potential for data-losing error conditions when recovering from a low power state like suspend or hibernate. In the future, there will be native SATA solutions which will solve many of these problems and will at the same time offer a real power savings benefit which should increase battery life.

Cost and Capacity This can't be overlooked. There is no question that SSDs cost more and are not available in as large capacities as standard hard disks. Today 32GB drives are common with 64GB starting to appear. Even the 32GB drives are extremely expensive, somewhere around $600. 64GB goes for much more. With time, that cost will drop and the available capacities will increase, but for most customers these are prohibitively expensive and too small right now. For others, the cost is nothing in return for the increased reliability they would gain. For example, I'm sure the Williams Formula One racing team that Lenovo sponsors would gladly spend the money for the increased reliability of a solid state drive in a high-vibration environment. SSDs will take the notebook world by storm. It just won't be quite as fast as many people think. Our engineers are optimistic that current limitations will be overcome. Data is THE most important part of any notebook and we want to be sure that customers can continue to be satisfied with their ThinkPad investments.