The original usage of the term solid state (from solid state physics) refers to the use of semiconductor devices rather than electron tubes, but has in this context been adopted to distinguish solid-state electronics from electromechanical devices as well. With no moving parts, a solid state drive is usually more robust, effectively eliminating the risk of mechanical failure, usually silent, and usually enjoys reduced seek time and latency by removing mechanical delays associated with hard disk drives.
A SSD is commonly composed of either NAND flash non-volatile memory or DRAM volatile memory.
Most SSD manufacturers use nonvolatile flash memory to create more rugged and compact alternatives for the consumer market. These flash memory-based SSDs, also known as flash drives, do not require batteries, allowing makers to replicate standard disk drive form factors. In addition, non-volatility allows flash SSDs to retain memory even during sudden power outages, ensuring data retrievability. Though flash SSDs are significantly slower than DRAM, they still perform better than traditional hard drives in regards to reads. Flash SSDs have no moving parts, eliminating seek time, latency and other electro-mechanical delays inherent in conventional disks.
SSDs based on volatile memory such as DRAM are characterized by fast data access, and are used primarily to accelerate applications that would otherwise be held back by the latency of disk drives. DRAM-based SSDs typically incorporate internal batteries and backup disk systems to ensure data persistence. If power is lost for whatever reason, the battery would keep the unit powered long enough to copy all data from random access memory to the backup disk. Upon the restoration of power, data is copied back from backup disk to RAM and the SSD resumes normal operation.
Solid State Disk (SSD) Architecture on the basis of FRAM
(ferroelectric RAM)
In Fig.1 show SSD block diagram. It includes the following main blocks:
· Interface controller, which service the standard interface for a link between the PC and the SSD.
· Processor system, which govern the total functioning of the SSD by synchronizing the flow of information exchanged between the FRAM block and the interface controller.
· FRAM block, which store the information that has been written
Function
SSD includes a controller that incorporates the electronics that bridge the NAND memory components to the host computer. Some of the functions include: Error correction, Bad block mapping, Read and write caching, Garbage collection and Encryption SSD manufacturers use non-volatile NAND flash memory in the construction of their SSDs (Since 2009) due to the lower cost compared to DRAM and the ability to retain the data without a constant power supply, ensuring data persistence through sudden power outages. Flash-based SSD typically uses a small amount of DRAM as a cache or buffer, similar to the cache in HDD. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating. The higher performing in SSDs is a capacitor or some form of Battery or super capacitor. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped Host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is generally one of the interfaces found in HDDs. They include: Serial ATA, Serial attached SCSI , PCI Express, Fibre Channel and USB.
Advantages
Firstly, SSDs are faster startup as no spin-up is required. Since there is no read/write head to move, they have typically near-instantaneous random access speed. SSDs seek times are orders of magnitude smaller than the best current hard disk drives so that they have extremely low read and write latency times. Also, because hard disk seeks are the limiting factor, SSDs have faster boot and application launch times. SSDs have lower power consumption and heat production and no noise because lack of moving parts making the SSD completely silent. SSDs lack of moving parts almost eliminates the risk of mechanical failure. SSDs are tougher than traditional hard drives. These features are useful for laptops, mobile computers, and devices that operate in extreme conditions.
Unlike hard disk drives, performance of SSDs is almost constant and deterministic across the entire storage. Traditional hard disks size and weight per unit storage are still better.
Disadvantages
As of early 2008, flash memory prices are still considerably higher per gigabyte than those of comparable conventional hard drives. Though currently far lower than that of conventional hard drives, SSD capacity is set to increase rapidly. SSDs are more vulnerable to certain types of effects, including abrupt power, magnetic fields and electric/static charges compared to normal hard disks.
Flash storage will wear out after 300,000-500,000 write cycles, while high endurance Flash storage is often marketed with endurance of 1–5 million write cycles so that SSDs are limited write cycles.
Comparative Analysis of SSD and HDD
Power consumption in regular hard drives consume larger power than solid-state drives. Most of the power in a hard drive is used by the motor that has to spin the disk. Faster performance in a hard drive requires faster rotational speeds and power. The SSD offers an enormous advantage over hard drives in power efficiency.
Performance wise, Flash has the advantage of lightning fast access time, well below 1ms, which is much faster than hard drives. Moreover, SSD drives support even faster sustained read and write speeds than the fastest hard drives.
In addition, SSD drives weigh only about half as much as a hard drive. Super Talent offers SSDs with plastic and aluminum casing options. The plastic casing option offers extreme light weight. Either way, solid state disks are lighter than hard drives because they don't have a motor.
Market Segments
Notebooks
1. Home users prefer notebooks to desktops because they can use their computer in any room. Thus, battery life is important since people will not want to carry their DC power supply around with them.
2. Business User à Frequent fliers for business, these people need something that is ultra-portable and a long-lasting battery life. Notebooks that incorporate SSDs weigh less and consume less power.
Web Servers
Another application area is for web servers. The SSD has excellent sequential read transfer performance and a web server’s job is to serve many small files very rapidly.
Industry
Any industrial products that require tolerance to extreme environmental conditions
1. ATM’s
2. Parking machines
3. Ticket vending machines
4. Factory automated machines
5. Medical Equipment
Questions
Q. Do SSD have any development of space?
A. Yes, but not too large, because SSD have more expensive price than other hard disk. Unless SSD have a breakthrough which is about development, otherwise SSD can’t substitute other types of hard disk.
Q. How about the lifespan of SSDs?
A. The file systems or firmware designs can mitigate this problem by spreading writes over the entire device (so-called wear levelling), rather than rewriting files in place. This problem is being improved all the time with lifespans increasing. Today's drives can last up to 20 years with average usage.
Q. Which two types of cell inside SSD?
A. Lower priced drives usually use multi-level cell (MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory. This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms, and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.
Q. Which types of SSD do you know?
A. The first type uses flash memory, and the second type that uses RAM (Both SRAM and DRAM), also known as Random Access Memory.
Both of these drives are better than standard hard drives, but they work in different ways.
Reference:
http://www.supertalent.com/tools/ssd.php
http://hi.baidu.com/yanyulou/blog/item/eae50d244a69da36c995594d.html
http://ecet.ecs.ru.acad.bg/cst/Docs/proceedings/Plenary/P-2.pdf
