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What is PCIe SSD?
A PCIe SSD or Peripheral Component Interconnect Express Solid State Drive, refers to a high speed expansion card that uses flash memory like other SSDs to store apps and files.
PCIe SSDs access the PCI Express slot of the computer and do not use the SATA chipset interface of the motherboard to communicate. These SSDs come with their own in-built storage controller that uses a driver unlike standard SSDs.
KEY TAKEAWAYS
- The PCI Express SSDs come in different versions and usually have 4 to 8 lanes but have the potential to perform much better than a traditional SATA or SAS SSD.
- The PCIe SSDs can be used as an alternative to server and enterprise-side flash employment and offer a much faster performance due to their low latency.
- Using PCI Express SSDs will not require sharing the bus because the flash is directly integrated on the PCIe interfaces and server motherboard and use their own serial link to connect to the host.
- PCIe SSDs offer faster loading of games and normal files, faster completion of intensive tasks, a lower boot time and a higher data transfer rate.
- Ensuring end-to-end data protection minimum latency and higher throughput, reduced cost of ownership, lower carbon footprints and production costs are some serious challenges faced in making the PCI Express SSDs.
Understanding PCIe SSD
Typically, there are different form factors of SSD drives such as SATA, PCI Express, and M.2.
Out of all these three types, one of the least popular ones is the PCIe SSD and therefore are least used.
One of the most significant reasons that the PCIe SSDs are not used widely is that these SSDs typically do not help in booting an older board.
It can only be used as a secondary storage.
Still, the PCIe SSDs are considered to be high-speed expansion cards that can attach different peripherals to the computer.
This is because these SSDs typically do not use the SATA chipset interface of the motherboard to communicate between the Windows files and the SSD.
Instead, these storage devices come with their own controllers built in which is significantly different from the controller chips that you find in other regular SSDs.
This specific aspect makes the PCI Express SSDs so unique.
This is because the storage controllers of the PCIe SSDs use a driver that is provided either by the operating system itself or by the manufacturer.
You will simply have to install this driver to use it.
At this point, you should note that the PCIe SSDs are not similar to the SATA drives in any way, though there is more than one aspect in them that are similar.
Depending on the conditions, you can connect the PCIe SSDs to the motherboard of your computer in more than one ways such as:
- Through a standard PCIe slot
- Through an M.2 slot or
- Through a U.2 adapter card and cable.
Ideally, irrespective of the ways you connect the PCIe SSDs to your computer, the fact that it eliminates the need for an SATA interface enhances its performance by a significant margin as compared to other regular SSDs.
This is because, the SATA interface, as of now, typically has 10 channels at the most but the PCIe interface has a maximum of 25 channels, and a few specific models even come with as many as 32 channels in them.
The higher number of channels helps it in caching and buffering applications.
It also makes the PCIe a multipurpose bus that can transfer all types of data through it to the processor.
You will also get a few non-standard PCIe SSDs that do not use a normal x4 interface but rather use an x8 PCIe slot interface.
These specific PCIe SSDs use a dual set of NAND chip assemblage with their own controllers and therefore can be configured as RAID 0 arrangements.
There are also a few other types of such storages available but it is less likely that you will ever come across these.
The format specs of the PCIe-based storages are developed and preserved by the PCI-SIG or the PCI Special Interest Group.
There are different versions of PCI Express released by them after PCIe 1.0 and 2.0 such as:
- PCIe 3.0 in November 2010
- PCIe 4.0 in 2017
- PCIe 5.0 in May 2019 and
- The PCIe 6.0, also called the Version 0.71, slated for a mid-2023 or early 2024 release.
Add to that, there is also the PCIe NVMe SSDs available that comes with Non-Volatile Memory Express protocol which offers a perfect and optimal command set to access the storage.
The performance is further accelerated and bettered due to the parallelism exploited by this specific PCIe standard.
However, irrespective of the types or version, the PCIe SSDs can overcome the bottlenecks that are typically related to the SAS or SATA based SSDs.
It is due to the number of PCIe lanes in each SSD which is proportional to the data transfer speed.
For example, 16-lane PCIe SSDs based on PCIe 3.0 specs can support about 32 gigabytes per second.
On the other hand, a SSD that comes with a SATA III controller can offer a data transfer speed of up to nearly 600 megabytes per second.
Still, in spite of the different versions of the PCIe SSDs, these are not very easy to break down.
One reason to say so is that the version 2.0 interface is found in most of the motherboards today in spite of the fact that the version 3.0 is newer than that.
Then, there are the PCI Express lanes that you will also have to factor in because all PCIe connections are divided into several lanes.
You will get a 4-lane, 8-lane, or a 16-lane socket and each of these can be identified by the size on the board.
The ones with 16 lanes are quite large and can be used to plug in a graphics card.
The number of lanes indicates the speed and performance of the device.
For example, in a PCIe 3.0, the theoretical speed per lane is about 1 GB/s, which means that the PCIe 3.0 x16 will offer a speed of 16 GB/s. That is quite a high speed.
However, usually the PCI Express SSDs are more common to have and use 4 or 8 lanes but even then the potential of these are quite high and better in comparison to SATA.
The real magic in the PCIe SSDs is in the elimination of the middlemen because the PCIe SSDs directly go into the PCI Express bus though there is some kind of a controller.
Therefore, the PCIe SSDs are those that offer faster performance than other SSDs but such benefits come at a cost.
For example, the PCI Express 4.0 compatible Samsung 980 Pro can attain a read speed of up to 7,000 MB/s which is double the speed of a PCIe 3.0 SSD and as much as 12.7 times faster in comparison to the standard SATA SSDs.
The PCI Express SSDs are the most innate fit for server and enterprise applications.
Though it is good to use by individuals as well, as of now, it might seem to be a bit overkill for standard computers.
Therefore, using the PCI Express SSDs may not be an option for anyone who is not used to transferring gigabytes and gigabytes of data or files every day and to whom every second matters.
For them, the SATA III SSD option would be far better and productive to go with since these devices are able to handle almost any job that is thrown in their way quite quickly.
It is mainly the point-to-point connection as well as the use of the faster PCI Express interface that reduces the latency and at the same time increases the speed of data transfer.
Moreover, the functionality of the PCIe SSDs is further enhanced by its use of two different pairs of signals for sending and receiving data from the SSD to the computer system.
These are called the ‘lanes.’ Each of these signal pairs comprises two wires, one of which is used for receiving data and the other is used for transferring data.
This means that each of the lanes consists of four wires.
It is this design and construction of the lanes that helps a single lane to receive as well as send 8-bit data packets at the same time.
Usually, as said earlier, a PCI Express interface can have as many as 32 different lanes depending on its design and you can choose from a wide variety of lanes starting from a single lane to 4, 8, 12, 16, or 32 lanes.
It is needless to say that the more the number of lanes in a PCIe interface, the higher will be the read and write or data transfer speed.
However, keep in mind that it will determine the price of the PCI Express SSD as well.
So, a PCIe x32 SSD will be more expensive and faster in performance as compared to a PCIe x1 SSD.
Here x1 and x32 denote the number of lanes of the PCI Express interface.
The PCI Express SSDs come with a lot of features that are useful to enhance its performance. Some of the most important ones are as follows.
Using a PCI Express will offer a near-instant boot time. As it is, the SSDs do not have any moving mechanical parts inside it and therefore usually boots pretty fast.
However, the PCIe SSDs use a dedicated P2P connection which reduces the boot time making it almost instantaneous if the operating system of the computer is loaded in it.
A PCI Express SSD will communicate with the CPU or Central Processing Unit directly, as said earlier, much unlike the SATA SSDs.
This is because the PCI Express SSDs do not need to depend on the RAM or Random Access Memory of the computer for it.
This also helps in improving the read and write speeds of the device and at the same time enhances the performance of the host device overall.
Just as the lanes enhance the speed of data transfer these also reduce the delay between the command and response.
Typically, the PCI Express SSDs come with a very low and very impressive delay time which is as low as about 2.8 microseconds.
The Power Failure Protection allows shutting down the device safely in case of any power failure.
This is a very important feature since it helps in protecting the data stored in it as well as in preventing the data from being corrupted.
The PCI Express storage devices are also able to implement the NVM Express logical interface.
This allows using internal parallelism which provides much quicker I/O operations.
These devices also can implement AHCI or Advanced Host Controller Interface logical interface. This offers backward compatibility.
With the advent of new PCI Express versions and the continuous development in the technology, it seems the PCI Express SSDs have a very bright future.
However, there are a few challenges to overcome, which is discussed at a later section in this article, and some existing flaws that should be taken care of by the manufacturers for that matter.
For example, the PCIe Gen 5.0 SSDs are larger than the previous models, which is a good aspect in a way that it enhances the performance and reduces the cooling needs, but then it comes with one major flaw – compatibility.
The larger size of these specific PCI Express SSDs is due to the M.2 25110 SSD form factor but the 22 mm wide and 110 mm long size creates incompatibility with the motherboards of today.
This affects the adoption of these larger PCIe SSDs.
Then, the PCIe 5.0 SSDs are also there to take into account. These latest versions of PCI Express has also gained a lot of attention from the users since its release,
This is because it is claimed that the Silicon Motion SM2508 controller in it can help the read speed of it can reach up to 14 GB/s.
However, the write speed can be a bit lower than that, clocking up to 12 GB/s.
In comparison, the PCIe 4.0 SSDs like Samsung’s 980 Pro, which is considered to be a high-end SSD, can barely meet half that mark.
Therefore, the PCI Express 5.0 SSDs will be a good choice for the data centers and servers.
With all these features and useful functionalities, the PCI Express based storage devices are gaining an increasing traction among the users who work with in-memory workloads and performance intensive applications. And, this even includes Machine Learning.
The PCI Express SSDs are also a favored option for those users who are engaged with high performance rendering jobs and data analytics, all due to its lower latency.
Whether it is a PCIe 3.0 or PCIe 4.0, the remarkable bandwidth and doubled output facilitates much faster data transfer between the SSD and the computer system through the PCIe interfaces.
Especially in the case of the PCIe 4.0 the two-fold increase in bandwidth has enabled the controller to contribute chiefly to the low-loss dielectric resources.
And, while the PCIe 6.0 based SSDs are upcoming, you can expect to have much faster SSDs in the future, once again, due to its double bandwidth.
Though it still has a long way to go in order to replace the PCI Express 5.0, the specs of the PCI Express 6.0 are already finalized by the PCI Special Interest Group.
They promise that it will reach a hypothetical highest bidirectional speed of up to 256 GB/s on an x16 slot, with 128 GB/s in one direction.
With such a tall promise, you can expect the PCIe 6.0 SSDs offer a high speed of up to 28 GB/s in the near future.
It is believed that the signaling technology in the PCIe 6.0 has been revamped and it will help it to achieve exceptional gains in bandwidth and at the same time maintain an extremely low latency.
According to a statement of Anandtech, this is considered to be the most significant move which is also arguably the biggest in the standards of PCIe in its entire history.
The architecture of the PCIe 6.0 will also do away with the incompatibility issues that are associated with the earlier generations of PCI Express.
This architecture is specifically designed to work well and perfectly with the existing hardware and use the previous specs so that it is perfectly functional with a PCIe 6.0 host.
Most importantly, this particular technology is expected to help a great deal in the adoption and transition to this new technology.
However, all these will take some time because as of now even the PCIe 5.0 is considered to be in its infancy.
It is still being verified with the enterprise-grade SSDs. Therefore, the PCIe 6.0 hardware will not hit the market any time before mid or late 2023.
Still, as the news is going round, a lot of servers have already started to contemplate using this new spec and are getting ready to use it when it is released sometime in the near future.
Till then, it is quite natural that you will continue to hear a lot about the PCIe 5.0 SSDs all through 2022.
Uses
The PCIe SSDs are typically used by those people who want fast performance and a very low latency.
The PCIe SSD storage acts as a substitute to a server-side flash deployment.
This means that it is good to use the PCI Express SDDs in enterprise and server applications.
It is the PCIe interface that performs as the underlying layer for data transport typically on add-in cards and graphics cards.
It also allows connecting different devices.
Benefits
A few of the prime benefits of the PCIe SSDs is that these unconventional server-based high performing drives offer higher speed, better compatibility, and larger storage capacity.
Also, the PCIe SSDs eliminate the need to share a bus since they integrate flash directly on a PCIe interface and a server motherboard.
This helps in connecting to the host via their own serial link.
Then there is the point-to-point architecture of the PCIe SSDs that improves the data transfer speeds and reduces latency between the storage and a server.
All these enable the PCIe SSDs to perform much better in comparison to a SATA, a SAS SCSI or Serial Attached SCSI, and Fiber Channel SSDs.
This is primarily because the PCIe SSDs take the functioning of the SSDs a step further by using the highest bandwidth channels in the computer which offers amazingly fast speeds.
And, with the advent of the 12th Generation Alder Lake Systems of Intel, there are new generations of such storage systems such as PCIe 3 SSD, PCIe 4 SSD, and PCIe 5 SSD.
The benefits offered by these PCIe SSDs are:
- Near-instant loading of normal files
- Fast completion of disk-heavy tasks usually within a minute or two if not in a few seconds
- Faster loading of games
- A much higher data transfer rate and
- A much lower boot time which is often limited to a couple of seconds.
If the PCIe SSD belongs to the latest version then you will also have a much higher bandwidth because the amount of bandwidth available in each PCI Express lane roughly doubles in each version.
This will translate into faster storing and loading speeds of games and videos and faster graphics rendering for high resolution videos and modern games.
However, everything is not good for the PCIe SSDs. These are quite expensive and maybe all motherboards may not support it.
Add to that, another drawback is the absence of regular storage commands which needs the manufacturers to create a custom software driver for the operating system.
Also, power consumption is an issue for CPU or RAM intensive tasks.
Still, the latest versions of the PCI Express SSDs are good to use in a computer and make it future proof.
Challenges
There are quite a few challenges faced by the manufacturers of the PCIe SSDs which, when overcome, will make these devices more popular in the future.
One of the most significant challenges is creating an inherent end-to-end data protection aptitude in these systems that will be clear to the end users.
Also, it is required to ensure that such a system offers a minimum impact on the latency and throughput.
Another significant challenge is ensuring a less significant carbon footprint as well as a reduced total cost of ownership.
That is not all. The manufacturers also need to find ways to reduce the production costs to make the PCIe SSDs much more affordable to the users and look seriously into the time to market without compromising with the interface homogeny.
It is also found that even after the launch of the 12th generation Alder Lake processors of Intel, the PCI Express SSDs lag behind in taking the fullest advantage of it.
Since pushing large amounts of data at high speed involves high power consumption, maintaining a safe operating temperature is another significant challenge.
This, along with the area and system latency challenges, are the key parameters of concern for the manufacturers which forces them to reconsider, if not re-architect the design.
However, the design itself is creating a lot of challenges down the road since it is getting more complex than before to add more features and functionalities, of which the most important is security.
Add to the design and size, the timing complexity is also increasing the challenges for the manufacturers.
Single stack or single row/single column orientation or multi-link bifurcation with double stack orientation may help in the performance of the systems but that needs exhaustive knowledge and tools to implement, adding to the challenges.
Then there is the typical challenge of overcoming the performance issues that arise from the lack of careful coordination between the host interface and the flash interface.
Some amount of parallelism is required to achieve the desired performance level. Multiple dice should be programmed so that they return the results at once.
Also, specific techniques such as native command queuing, block picking, and garbage collection must also be balanced in order to achieve a high performance through parallelism.
However, at the same time it should be kept in mind that the power envelope of the SSD is not exceeded.
The flash cells hold some amount of voltage which may get altered when the controller makes a request for the voltage from the cell when it is read too many times.
This is called read disturb management and this needs to be monitored and managed so as to determine the number of times a cell can be feasibly and effectively read.
When it is found that a particular cell has been read too many times, the data in that specific cell can be transferred to another cell which will start the cycle clock counter from the beginning.
However, it is quite a difficult challenge to know when and how to move the data from one cell to another when the read times surpass the preset threshold.
This is because if too little data is moved, you may end up losing data and if you move data every now and then more than that is necessary it will add to write amplifications and reduce the performance level.
Apart from that, temperature management is another challenge. If this is not controlled properly and timely, the controller or the flash memory will become too hot and may even burn out too early.
It is therefore needed to understand the behavior and temperature of the whole drive to mitigate the impact.
Writing seems to draw the most power and heat things up excessively and quickly.
Once again, the controller needs to monitor the temperature and slow things down and control the power consumption, especially writing, to ensure that the temperature level does not cross the preset threshold.
Here lies the challenge. Ideally, it is pretty difficult to regulate the write speeds of the drives without immobilizing writing on the whole.
In order to ensure that the writing activity does not stop entirely, the controller needs to take into account several different temperature thresholds and constrict the writing performance.
Designing a proper firmware for endurance is another significant challenge but it is extremely necessary to ensure that the controller is able to write but there is no write amplification. This will help the drives last longer.
Apart from that, life curve throttling should also be used in order to augment the write performance.
This particular technique involves tracking the amount of data that needs to be written in a particular time period.
This is typically done by the debits and credits system.
If it is found that the drive has accumulated a lot of debits, so much that the life span of the drive is threatened, it will automatically slow down the drive.
After this process is completed successfully, the write performance will be throttled back just as required.
However, the problem here is that most fundamental SSD controllers are typically not compatible with this process of live curve throttling.
These controllers of the drive simply restrict the total amount of writes sent to it over its lifespan.
And, this is very difficult, if not impossible, to track it manually and restrict the traffic to the drive.
In order to maintain a consistent performance level, the flash vendors however are contemplating on the erase part of the cycle.
Add to that, adding newer and better flash managing features will also optimize the performance.
Perhaps, one of the best ways to improve the performance is to incorporate data protection and data integrity routines.
When these challenges are overcome, you can expect to see more and more users choosing better and more reliable storage options in the form of PCI Express 5.0, 6.0, and NVMe based Solid State Drives.
Conclusion
Coming to the end of this article, now you surely know how useful the PCI Express Solid State Drives are.
Though there are a few specific challenges to overcome by the manufacturers, these alternative storage options provide a lot of benefits to the users.
