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PCIe Gen4 is now mainstream, and Gen5 is just around the corner. So why are PCIe Gen3 SSDs still so prevalent?
While it is true that PCIe Gen4 M.2 SSDs deliver a very high level of read and random I/O performance, write performance will inevitably degrade over time. Performance can drop sharply after the initial write session; from 5000+ MB/s to the 2000MB/s range, after only using 10% of available capacity; around 100 to perhaps 200MB/s faster than Gen3 SSDs of the same class.
Now, it’s worth pointing out that for general use, or say an NVMe configuration designed to support a specific piece of software or utility, this may not even be considered a penalty. These kinds of applications benefit from reduced access times and superior random I/O capabilities. Gen 4 SSDs are an ideal match.
That said, many business, industrial, R&D and scientific applications prioritize sustained write performance, and tend to need a lot of storage capacity (a lot of SSDs in other words). They depend on solutions capable of delivering consistent levels of transfer speed over prolonged periods of time. Databases, online transaction servers, IOT solutions, security systems – all of these often run around the clock, and require predictable, repeatable transfer bandwidth to function optimally.
Simply put, for such applications, the majority of commercially available Gen4 SSDs offer no major performance benefits over Gen3 models. And, when you take cost and capacity into consideration, some PCIe Gen3 SSDs may in fact, be a better overall solution for these environments.
Getting the most bang for your buck: Gen4 Controller + Gen 3 Media
Although on the surface, it may seem like and odd pairing; using “slower” drives with a “faster” controller, coupling Gen3 NVMe SSDs with a Gen4 NVMe controller is actually rather common. Initially, many invested in Gen4 controllers as a future-proof solution. However, early adopters quickly realized this combination allowed them to fully utilize Gen3 NVMe SSDs. 14,000MB/s wasn’t just a best-case scenario, it was easily obtained due to PCIe host bandwidth upgrade, especially if you opted for an 8-port controller, such as our SSD7540.
In short, depending on your application and the type and capacity of NVMe SSD you settle on, the performance tradeoff is minimal. In contrast, the cost savings can be considerable – you can save 30% or more, per SSD of the same capacity if you simply opt for the Gen3 “downgrade”.
Several classes of NVMe media stand out in particular – datacenter, server and NAS class M.2 SSDs. They combine solid long-term sustained write performance with a high level of storage capacity, relative to M.2 media (up to 4TB). In addition, many model lines benefit from enterprise level features, such as PLP (power loss protection), and are long-lived, with operational lifespans measured in disks-writes-per-day (DWPD), rather than the universal total-bytes-written (TBW).
As suggested by their class designations, PCIe Gen3 Datacenter and NAS class M.2 SSDs were developed for business and industrial server applications. Although often marketed as “caching” solutions, they are quite capable of functioning as actual storage devices, and are often a cost-effective and compact alternative to U.2/U.3 based solutions.
Based on extensive benchmark sessions that have been conducted using a variety of test platforms, we’ve determined NAS and Datacenter class SSDs are capable of maintaining, on average, 1800MB/s of transfer performance, even after 90% of available capacity has been used. Additionally, this transfer rate remains consistent whether the SSDs are used singularly or configured into RAID arrays.
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