SSD - Solid State Drive

Everybody these days seems to be in a hectic dash against time. People roll their eyes back in their heads giving the nastiest of their frowns if even by mistake we mention about ‘legacy systems’ for the simple reason that they are sluggish, unreliable and inefficient. The digital data is doubling and quadrupling exponentially day after day. To cope with this trend storage-solutions need to be devised that can not only store but also transfer terabytes of data in a matter of a few hours or less; of course at the same time being energy and space efficient. Engineers across the globe pledged to incarnate just such a device and what is more they actually did!

Working principle of device:

Solid State drives (SSDs) are robust, energy efficient and quite drives that can be used with the smallest form factor computer. They do not contain any moving parts on the inside as did the traditional HDDs (Hard Disk Drive). Since they don’t contain any parts that move, the heat and sound production as well as the energy consumption drop dramatically. These petite drives can find their way (just the way cats shrink and wiggle into tight spaces!) into devices where space and battery are at a premium. Their performance is simply breath-taking! That tottering turtle of Bob’s cubicle can be turned into an insanely fast rig by simply swapping an HDD for an SSD. But the question that must naturally arise is that, “what makes these SSDs work at the speed of light?” Well L1, L2 and L3 (Static RAM) cache have access times of 10ns or lower. The figure rises to about 40ns in the case of main memory (Dynamic RAM). This difference may not be perceptible unless one is using time critical applications. However, the access times of HDDs are measured to be in the order of milliseconds (9-12ms) which is almost a million times slower than both the cache and the main memory. This implies that the HDD will prove to be the bottleneck in a system. Unless there is a way to retrieve the data stored at blazing fast speeds the performance of the computer will suffer, no matter how fast and powerful the squad of Memory, cache and the CPU is! SSDs boast of an average access time of about 0.1ms making them almost a hundred times faster than HDDs (Note: access times and transfer speed in MB/s has no correlation whatsoever. The fastest SSDs can transfer files only up to 10 times faster than HDDs)!

SSDs have electrical grids (flash memory chips) that are partitioned into what are called pages. The pages are where the data are stored. The pages are grouped together to form blocks (similar to sectors and clusters and in case of HDD). Data are written to an empty page only and it is possible that not all the pages of a block are filled. It bears repeating that an SSD cannot overwrite data the way HDDs do. The blocks need to be reset before the next write operation can occur (Thus before copying new data old data need to be deleted). Overtime due to the successive write operations the presence of contiguous empty blocks reduces increasing the number of scattered empty blocks. Thus large files can easily get scattered to blocks that aren’t contiguous which increases the access time, a deleterious upshot of course! It may also happen that all the blocks have been written to but only partially thereby efficiently wasting the available precious space! Thus to reclaim the lost empire the SSD will move the data off the blocks and to a buffer memory and then reset the blocks. Once the blocks have been reset the data present in the buffer gets copied back to the drive. These procedures are time consuming by nature.

Thanks to TRIM! TRIM enabled SSDs can make the operating system locate specific pages where the data is stored and then delete them. This will obviate the need to erase and re-write data over large memory blocks reducing the wear on the flash memory considerably. This ensures the longevity of the drive. TRIM feature also instantaneously deletes the data from the pages instead of waiting to delete it until the next write operation. This increases the speed of copying files the next time after data has been deleted. Thus TRIM is a boon in disguise for modern SSDs. It must be noted that SSDs do not need to be defragmented.

Manufacturer of device, its models and prices:

1.      Samsung – 960 EVO 1TB (M.2) (Rs. 39,000), 850 Evo (SATA) (Rs. 7,060), Samsung External 2 TB SSD T3 (Rs. 60,856) etc

2.      Intel – SSDPECME016T401 DC P3608 Series 1.6TB (Rs. 4,44,957), Intel 240GB Intel 535 2.5" (Rs. 11,999), Intel 2500 Series Solid State Pro Drive SSDSC2BF480H501 (2.5" 480GB, SATA 3 (Rs. 34,406) etc

3.      Sandisk – SanDisk Ultra II 480GB SATA III 6Gb/s Internal (Rs. 17,500), Sandisk Extreme PRO SDSSDXPS-480G (Rs. 16,174), SanDisk Extreme 900 SDSSDEX2-1T92-G25 2TB External (Rs. 85,999) etc

4.      Seagate – Seagate Nytro XF1230-1A0480 480 GB 2.5" (Rs. 34,2479), Seagate 1200 800 GB 2.5" Internal Solid State Drive ST800FM0043 (Rs. 57,957), Seagate 600 SSD 480 GB SATA 6 Gb/s 2.5-Inch (Rs. 40,206) etc

5.      WD – WD 240GB Green SATA III 2.5" (Rs. 6,249), WD 120GB Green SATA III 2.5" (Rs. 4,299) etc

 Standard Configuration of device: SSDs could be either flash based or DRAM based. Flash based SSDs these days, use NAND flash memory chips (non-volatile) and are slower than DRAM (volatile) based SSDs. DRAM SSDs need to have an external power source or an internal battery. Since DRAM is volatile in nature as soon as the power is switched off the contents from the DRAM need to be transferred to another backup medium inside the SSD case. This calls for the extra battery/power supply. The battery will power the DRAM until all of its content gets transferred to the backup medium. When the power is switched back on the contents from the backup are copied back to the DRAM. This process occurs on every power cycle that the SSD goes through. NAND SSDs often use small amounts of DRAM as a cache. Frequently used data is stored in the DRAM cache and thus it results into an overall performance boost.

SSDs can use several interfaces. Common ones include SATA (1.8, 2.5, 3.5 inch), USB, Thunderbolt v3, and M.2 (usually it is PCIe 3.0 x4 for consumers. PCIe 3.0 x16 could also be used to insert some enterprise SSDs that have huge capacities and extremely fast speeds). SATA and M.2 SSDs can be used as internal drives while USB and thunderbolt drives can function as external drives. It must be noted that SSDs using PCIe x4 lanes or more are the fastest of all. 

Cost: DRAM SSDs are costlier than Flash based SSDs. Capacity, speed and endurance (in TBW – terabytes written or DWPD – drives writes per day are a measure of the amount of data that can be written to the drive before it will die) are directly proportional to cost of the SSD. Prices will drop as the time advances, as they have compared to the past decade. But for now SSDs are costlier than HDDs.

Market share of different models (Standard companies only):

l  Samsung

l  Intel

l  Sandisk

l  Seagate

l  Western Digital