SSD NAND – SLC, MLC, TLC, and QLC
The first differentiator for SSD relates to the NAND flash, which would either be SLC (Single Level Cell), MLC (Multi Level Cell), TLC (Triple Level Cell) or QLC (Quad Level Cell). The difference between the four is the amount of data stored per cell – with SLC it’s 1-bit per cell, with MLC it’s 2-bits per cell, with TLC its 3 bits per cell, and with QLC its 4 bits per cell. These differences in design impact performance, MDF, storage capacity, and most importantly price point, all of which are factors that determine which type of NAND is best for which type of application.
In general, because Single Level Cell (SLC) drives are less complex, they have longer MDF (10 times that of MLC and 20 times that of TLC), less storage capacity, better performance, and higher cost than other NAND. MLC, TLC, and now QLC NAND, however, offer far greater potential for SSDs because they deliver very good performance, high durability, low power consumption, and have the advantage of being able to store more bits per cell which increases capacity and lowers the cost per gigabit making SSDs more affordable. All of these advantages are driving SSD growth in all markets, including data centers, high performance computing, mobile computing, and so on.
3D NAND and V-NAND
As the demand for greater capacity in SSDs continued to grow, the traditional planar NAND was reaching its scaling limits, making it increasingly difficult to meet the need of more storage. With that came the introduction of 3D NAND, or V-NAND as it is called by Samsung, which uses an innovative technology to stack the NAND cells vertically to provide 3X the capacity. 3D NAND or V-NAND incorporates either MLC, TLC, or QLC NAND using the x,y and z axis to expand vertically.
Click here for a short video showing how 3D NAND Technology Transforms the Economics of Storage.
Optane Memory is a new type of non-volatile memory developed by Intel that is 10 times faster as well as 1,000 times more durable than NAND, and is 10 times more dense than DRAM and nearly as fast. Optane Memory is a radically different technology from standard NAND in that it is a transistor-less design where data is written at a bit level by applying different voltages to change the physical state of the cell. This more efficient design increases performance, improves durability, enhances storage capacity, and helps lower power consumption. For mor information on Optane https://www.asipartner.com/solutions/server/intel-optane-technology/
Storage Capacity & Durability
Since SLC, MLC, TLC, and QLC take the same amount of drive space, increasing the bits per cell increases the density, as well as the storage capacity and decreases the cost per gigabyte to lower the cost of the drive. There are, however, side effects to increasing the number of bits per cell because managing the bits and information is more difficult and the read/write logarithms are more complex. This added complexity decreases performance and reduces the write cycle endurance of the drive when comparing one NAND technology to the next. With that said, SSD drive manufacturers have integrated different techniques to boost performance, such as adding cache and utilizing advanced drive controllers. In addition, the manufacturer can improve the write endurance by using a technology called over provisioning, where a portion of the capacity is allocated to preserve write operations, or through a technique called wear leveling, which ensures that all memory chips are used before the first cell can written to again.
Shock and Vibration
Shock and vibration are major concerns for many computer users, particularly with notebooks, which are susceptible to damage resulting from sudden turbulence which can result in a loss of data. Since SSD drives have no moving parts, they can handle much higher shock and vibration, making them ideal for countless mobile applications. SSD drives are rated at 1000G/0.5ms, while the most durable hard drives, such as Seagate’s Extreme Environment drives, have ratings of 150G/11ms. There is obviously no difference in this case between MLC and SLC, and only between SSD and regular disk drives.
Because SSD drives use low power memory and don’t have any moving parts, their overall power consumption should be less compared to disk. Hard drives, however, particularly for notebooks, have been designed very well to consume less power, but this typically comes at the cost of lower RPMs, which can impact performance so there is a trade off that does not apply for SSDs. In general, SSD drives will extend your battery run time by about 30 minutes making them an ideal option for notebook users. Quiet, low power, fast, and durable!
The power savings associated with SSD drives is also a critical factor in data centers where SSD usage is exploding. At first glance, people may wonder why you would want to use more costly and lower capacity SSD drives in place of spinning disk drives, and the answer is more than just performance gains, it is also due to the power savings achieved by using SSD drives. Not only do SSD drives consume less power (about 2W on SSDs compared to 6W on HDD) but because they finish tasks quicker resulting in lower CPU utilization they help reduce the total power consumption of a computer. In addition, if you wanted to match SSD IOPs performance, a critical factor in data centers, with hard disk drives you’d need considerably more drives, which in turn consume more power and require more cooling which consumes more power. Now, imagine a data center with thousands of drives performing thousands of I/O intensive tasks that require high CPU utilization, and you can begin to see how the total power consumption of the data center can be driven down helping to lower operation costs. This is significant particularly since power costs are extremely high and only increase over time. So not only do SSD drives offer considerable performance benefits, the TCO (Total Cost of Ownership) is significantly lower.
Performance ratings can be very confusing with the multitude of programs that can be used to try to determine the speed of any particular product. Add to this the fact that not all products, including SSDs, are created equal, and that only adds to the evaluation complexity. SSDs do however dramatically outperform hard drives in just about every area except writes and sequential reads, but even this can change over time particularly as the hard drive begins to be populated with data, because unlike SSDs, hard drives suffer from performance degradation as they reach capacity because there is more data on the platters that needs to be reviewed or written around.
Drive performance is generally rated by bandwidth (MB/s), the amount of data that can transferred, and Operational Performance (IOPS), which is how fast the data is transmitted for both read and write tasks. Comparing bandwidth between HDD and SSD, the fastest hard drives transfer about 200MB/s, while SSD push the limits of the SATA port by transferring up to 550MB/s. In terms of IOPS, which measures how many times per second a drive is able to read or write data in a given time, is important for many types of systems particularly those that handle a lot of requests such as datacenters, servers, video, and so on. SSD drives perform astronomically better than spinning disks because the SSD drives controller needs very few times to locate memory address, so in the time it takes a HDD drive to perform one task, an SSD drive can perform 20 or more tasks depending on what disk drive technology is being used as the comparison. In addition, advances in technology, such as SSD drives that utilize the PCIe interface in place of slow SATA, offer even greater performance gains through improved throughput. With PCIe solutions, SSD drives are no longer restricted by the limitations of the SATA bus so they have the potential to reach their true performance capability.
MSATA and M.2
In their simplest form, SSD drives are basically a memory card packaged inside a metal case that makes them look like a familiar spinning disk drive and allows them to be easily installed in standard computer drive bays. However, this is not the only form factor used in computers for SSD drives. In fact, even the standard hard drive format has different options including 2.5” diameter drives that are either 7mm for thin devices, such as Ultrabooks, or 9.5mm thick for standard size form factors.
Due to their use of NAND memory, there are other form factors that allow SSD drives to be used in very thin systems, or as a secondary drive. This is a great benefit in many systems from small form factor PCs like the Intel NUC, to notebooks, and even AIO systems. The most common options for adding SSDs to these systems, other than by using a standard SATA interface, is mSATA or m.2 form factor. mSATA and m.2 devices are approximately the size of a business card and they connect to a mini-PCI-E port that in conjunction with the dimensions of the physical card help reduce the space needed to accommodate the drive. Many SSD manufacturers offer mSATA and m.2 products ranging in capacity from 32GB to 2TB or more.
With the desire to continue to reduce the width of computer devices came the need for lower profile storage and the ability to increase overall capacity, so Solidigm worked to create a new mSATA form factor now called M.2 (Formally New Generation Form Factor or NFGG). Despite the large capacities we saw with mSATA, manufacturers could still only populate the PCB with 4 NAND modules so there were limitations which impacted the overall capacity and increased the cost for higher GBs. M.2 SSD drives were designed to resolve the space limitations of mSATA, so they come in four different lengths ranging from 42mm to 110mm allowing them to accommodate more NAND to reach higher storage levels and reduce the cost per GB. Although all M.2 cards have the same standard connection in terms of width, they do have different lengths and different edge connectors or key types, so it’s important to make sure you select a card that is compatible with your system.
M.2 Dimensions: As mentioned above, M.2 cards are available in different lengths, and while some systems have mounts (Clip or Screw position) that will accommodate different size cards which give you more options, some are limited to supporting just one card length. Common terms for identifying the dimensions of M.2 cards include 22×42, 22×60, 22×80 or 22×110 where 22 refers to the width 22mm (Standard for all M.2 cards) and the second number refers to the length of the card in mm. You may also see the cards referenced as 2242, 2260, 2280, or 22110 for example.
M.2 Edge Connector or Key Type: The big advantage offered by mSATA and M.2 is that these SSD devices utilize the PCI-E bus rather than a SATA III connection. This allows for significantly better performance as a result of the increased throughput capacity. The overall performance, however, is determined by the number of PCI-E lanes used by the M.2 device which can be PCI-E x2 or PCI-E x4. The decision to do PCI-E x2 or PCI-E x4 is determined by the motherboard or mobile device manufacture so in addition to selecting an M.2 card length that is support by the device, you also need to select a card with an edge connector or keying type that is compatible. There are two M.2 Key types for the socket and three possible key types for the M.2 card.
A “B” Keying supports PCI-E x 2 for up to 10Gbits/sec while an “M” keying supports PCI-E x4 for up to 20Gbits/sec which is both significantly higher than the theoretical maximum of 6Gbits/sec of SATA III.
M.2 SSD cards are available in three different key types which include “B” keying, “M” keying and “B+M” keying. While “B” keying and “M” keying cards can only work in a similar socket, the “B+M” keying card can work in either a “B” keying or “M” keying connector so it is the most versatile in terms of compatibility. It is, however, important to note that “B+M” keying cards use PCI-E x2 so if they are installed in a “M” keying connector with PCI-Ex4 their maximum throughput will be 10Gbits/sec for PCI-E x2 performance, not 20Gbit/sec which is possible with PCI-E x4.
Most Common Connections: The most common keying types in the market are “M” keying for the connector (Some manufacturers use PCI-E x2 even with an “M” connector) and “B+M” keying for the cards. For customers that are pushing the performance envelop, you want to make sure you have a device that uses an “M” keying connector that uses PCI-E x4 and an “M” keying M.2 card.
E1 or EDSFF
E1 or EDSFF is a new form factor standard introduced by Intel that is commonly referred to as a “Ruler”. The form factor was designed for 1U rack server to maximize storage capacity, improve manageability, reduce power consumption, reduce thermals, and improve serviceability. E1 SSD form factors fit vertically in the rack server and come in different lengths as well as different widths depending on the version. They are hot swappable and utilize the PCIe NVMe interface.
||up to 25W – 38.4mm
||up to 40W – 38.4mm
|E1.S 8mm Heat Spreader
|E1.S Symmetric Enclosure
|E1.S Asymmetric Enclosure
|E1.S Asymmetric Enclosure
U.2 is a high-performance SSD designed to use the PCIe x4 NVMe interface in a traditional 2.5” form factor. The advantage of U.2 is you can install multiple drives since they fit in standard 2.5” bays, they have larger capacity, and they are hot swappable. The challenge with U.2 is they do require motherboards that have U.2 connections, and they require the proper cable with both a SFF-8639 connector for the drive on one end along with the U.2 jack on the other.
SSD drives can offer benefits to almost any user whether they are looking to replace their entire storage solution with SSD or use SSD as a boot drive to increase performance, but there are distinct markets that offer exceptional growth and value for resellers who introduce SSD.
Datacenters and Servers
The key determining factors in environments that have high data requests is total cost of ownership, which takes into account performance and overall operation costs, not just cost per GB. With datacenters or servers, replacing spinning disks with SSD drives can boost performance, while at the same time reducing or lowering power costs. Looking at this two ways, if we consider a standard server configuration we might consider the storage requirement in total capacity where we would have the same number of SSD and HDD drives to determine our comparison. With SSD drives, they have high IOPS so they finish tasks quicker, reducing the workload placed on the processor which lowers cost. They also require less cooling or nearly no cooling which reduces power consumption by illuminating extra cooling fans, and the drives themselves consume less power in full use (2W compared to 6W) and in ideal mode where they use 90% less power. The second way would be to consider a datacenter where IOPS performance is critical and you would want to try to match the performance of SSD using HDD. Since SSDs IOPS performance is 20 times or more higher than HDD, you would need considerably more spinning disks to achieve the same overall performance. Using the power saving rules previously mentioned, and you can see how power costs and space expense would be impacted. In terms of overall TCO, SSD offer a very attractive alternative.
HDD are not going to be replaced by SSDs anytime soon, simply because cost per GB is still a critical factor for many users and for many PC usage models, but that should not mean those users can’t benefit from adding an SSD to their system. System integrators that offer SSD drives as an optional boot drive or to create RAID configurations, as well as utilize motherboards that can support mSATA/M.2 SSD drives, can give their clients a better user experience and increase the value of their systems. Systems would boot faster, load the OS and other applications faster, run games faster, and so on. Just about every usage related to performance would benefit from an SSD drive.
SSD drives are a natural fit for notebooks, particularly now that capacities have gone up and costs per GB have come down. Of course notebook users would recognize the performance gains associated with using an SSD drive, but they would also gain longer battery life due to the lower power consumption, have less failures as a result of the higher shock and vibration tolerances provided by SSD drives, and would be quieter due to the lower heat dissipated by the drives. Additionally many notebooks offer mSATA or M.2 (NGFF) slots that would allow for dual SSD drives, RAID, and other storage options for notebooks that can’t be achieved using spinning disks.