Solid state disk (SSD) is about the hottest topic in storage these days as an alternative to traditional hard disk drives. There are several popular reasons given for changing over to SSD: Its lighter than traditional hard disk drives; has better I/O; greater durability, and lower power consumption. But should you consider SSD for your personal computer or laptop? Most experts, including vendors selling it, say no.
There are a host of problems with SSD, said Avi Cohen, head of research at Avian Securities in Boston. Theres no reason to pay the extra $600 to $800 or 40% to 80% premium for a solid state drive. No technology will make SSD viable [for notebooks and PCs] in the foreseeable future.
Cohen and others point to the fact that power savings through SSD use equates to an additional six minutes or so on your average laptop the monitor and CPU eat vastly more power than a computers drive, which is in sleep mode much of the time. Some independent online publications have actually shown SSD to suck more battery power than traditional hard disk drives.
Even vendors that sell solid state disk admit that when it comes to speed, theres little advantage at the consumer level (see Performance showdown: Flash drives versus hard disk drives).
For example, Pat Wilkison, vice president of business development at flash memory maker STEC, said the magnitude of performance in SSD products definitely varies. STEC sells high-end flash memory to enterprise-class storage companies such as EMC, which uses the product in its Symmetrix storage array.
The class of product EMC needs is fundamentally different from what notebooks need, Wilkinson said. The reality is that performance varies depending on the applications running on it. Random write speeds are horrible. And guess what? As PC users, writes are important.
Applications that require many random reads, but not sequential reads or writes see tremendous performance improvements on SSD over traditional hard disk drives. In fact, most experts agree that SSD is far superior to using high-end, 15,000rpm hard drive in Fibre Channel-attached storage devices.
According to Cohen, high-end flash drives outpace high-end Fibre Channel drives at a 20:1 price/performance ratio because businesses must as many as 20 15,000rpm hard disk drives in order attain the random read performance of a single solid state disk drive. For [the cost of] each short-stroke spinning disk drive you replace you could put 20 SSDs in, Cohen said.
Other than high-end storage arrays and servers, the only other place solid state disk belongs today is hand-held devices because their main purpose is reading data and high-end laptops such as Apples MacBook Air, and only because its cool, and not because of any performance advantage, according to Cohen.
Durability
While SSD does have a durability advantage over hard disk because there are no moving parts to break, the lifespan of flash memory varies greatly depending on a number of factors.
Among the factors differentiating NAND SSD memory quality is whether it is single-level cell (SLC) memory or multi-level cell (MLC) memory. SLC stores one bit of data per memory cell while MLC stores two or more bits of data per cell, affording it greater density, but slower data transfer speeds, higher power consumption and shorter lifespan. In general, SLC costs than MLC to manufacture and is sold for about twice as much as MLC memory, Coulson says.
But SLC vs. MLC isn't the only factor differentiating the quality of NAND memory. Some MLC memory is actually faster than SLC memory based on write amplification methods, which can boost raw flash chip performance but degrade longevity. Generally, the higher performance an SSD drive has the longer life it will have because of better drive efficiency.
But, the myth that SSD drives can attain the same longevity as hard disk drives is only true in enterprise-class devices that have sophisticated wear-leveling software in the drives controller that evenly distributes data across the device to ensure cells do not wear out prematurely. Common SLC memory used in laptops and PCs has about 100,000 writes per cell and MLC can have as little as 1,000 writes per cell, according to Joel Hagberg , vice president of business development for drive-maker Fujitsu Ltd.
Hagberg said his company does not plan to launch any solid-state disk-drive products over the next two years because the value proposition of the technology is not compelling enough and won't be until technology breakthroughs change solid-state disk's performance and reliability, as long as two years from now.
- Current SSDs consisting of NAND shoehorned into spinning disk drive form factors are limited in many ways and are probably hindering wider adoption
- The standards necessary to take full advantage of NAND and its capabilities within an SSD are just now beginning to flow through the various committees so full featured products probably wont hit shelves till mid '09
- NAND in the PC (on motherboard or PCI or whatever flavor) makes sense but requires MSFT to update OS to take full advantage of NAND's attributes. These changes were not included in the most recent service pack and contacts within MSFT have not heard of any progress coming in 2009. (It appears MSFT is more focused on increasing PC touch screen capabilities then NAND integration).
- A new standard needs to be established for measuring an SSD's effective life capacity rather then GB of storage so the promise of better SSD reliability over the course of the life of an SSD is more clearly defined and evaluated.