The external storage market has experienced rapid growth over the last few years, particularly in the retail consumer segment. The demand has been fueled by increased amounts of user-generated multimedia content and high-resolution artwork / assets for games that are better off being installed in external drives. The growth has mainly been in in bus-powered flash-based storage devices.
Thunderbolt SSDs are at the top in terms of both performance and price, but the last few years have seen various high-end portable SSDs with a USB interface. The USB 3.2 Gen 2×2 (20Gbps) ecosystem has been slowly gaining traction. Many device solutions have turned up in the retail market over the last couple of years – all of them have been based on ASMedia’s ASM2364 bridge chip, with a discrete PCIe 3.0 x4 NMVe SSD downstream of the bridge. While such configurations deliver on the 20Gbps promise, they are not particularly power-efficient.
The power efficiency aspect changed earlier this month with the introduction of the Kingston XS2000 portable SSD. Based on Silicon Motion’s SM232x family of USB Flash Drive (UFD) controllers, the product family offers full Gen 2×2 performance at a fraction of the power consumed by the Gen 2×2 SSD solutions currently in retail.
Looking to show off their new controllers, Silicon Motion sent across a bare reference board on which the Kingston XS2000 is based. The firmware used in the Kingston XS2000 and the reference design are pretty much identical, with the only difference being the absence of the casing and thermal solution. The review below presents a detailed evaluation report of the SM2320 reference design. Except for the analysis of the thermal design aspects / temperature profile, it also tracks what consumers can expect from the Kingston XS2000 portable SSD.
Introduction
External bus-powered storage devices have grown both in storage capacity as well as speeds over the last decade. Thanks to rapid advancements in flash technology (including the advent of 3D NAND and NVMe) as well as faster host interfaces (such as Thunderbolt 3 and USB 3.2 Gen 2×2), we now have palm-sized flash-based storage devices capable of delivering 2GBps+ speeds. Traditionally, these portable drives have fallen into one of the six categories below, depending on the performance profile and the components used.
- 2.5GBps+ class: Thunderbolt SSDs with PCIe 3.0 x4 NVMe drives
- 2GBps+ class: USB 3.2 Gen 2×2 SSDs with PCIe 3.0 x4 NVMe drives
- 1GBps+ class: USB 3.2 Gen 2 SSDs with PCIe 3.0 (x4 or x2) NVMe drives
- 500MBps+ class: USB 3.2 Gen 2 SSDs with SATA drives
- 400MBps+ class: USB 3.2 Gen 1 SSDs with SATA drives
- Sub-400MBps+ class: USB 3.2 Gen 1 flash drives with direct flash-to-USB controllers
At the 2021 CES, Phison introduced the U17 (USB 3.2 Gen 2) and U18 (USB 3.2 Gen 2×2) UFD controllers, which added additional categories in the above list – a sub-1GBps performance class using direct flash-to-USB 3.2 Gen 2 controllers and a sub-2GBps performance class using direct flash-to-USB 3.2 Gen 2×2 controllers. The Crucial X6 Portable SSD lineup was upgraded earlier this year to utilize the Phison U17 controller, but the U18 controller doesn’t seem to have hit retail yet.
Silicon Motion, on the other hand, was late to UFD party in terms of putting out their press release. However, they managed to get their design wins shipping along with the public announcement of their SM2320 and SM2321 controllers. The SM2320 USB 3.2 Gen 2×2 controller actually promises 2GBps+ speeds, while the SM2321 USB 3.2 Gen 2 enables 1GBps+ flash drives. These numbers seem to offer more than what Phison promises in the U17 and U18, though real-world testing is essential to compare the two controllers beyond the claimed marketing numbers.
The SM2320-based portable SSDs (and the U18-based ones, when they eventually appear for sale) represent the retail market’s first look at a non-ASMedia solution in the USB 3.2 Gen 2×2 device market. The advantages of a native UFD controller over a combination of a bridge and NVMe controller are self-evident:
- Reduced BOM cost, leading to lower retail price for the consumer products
- Reduced power consumption
- More space on the PCB to integrate additional flash packages for extra performance
- Reduced space requirements leading to more compact UFDs
- Integrated security features preventing hardware-based security attacks possible in a bridge chip / NVMe SSD solution
Silicon Motion sent across their 1TB SM2320 reference design for evaluation around the same time that Kingston started sampling their XS2000 portable SSD (based on the same board). While we were not on Kingston’s sampling list for the end product, the SM2320 reference design gives us quite a bit of insight into the XS2000’s operations.
The SM2320 board measures 62mm x 25.4mm x 5mm, and weighs a puny 7g. These are without the casing / thermal solution. The board is double-sided and contains four flash packages. A USB 3.2 Gen 2×2 Type-C cable was supplied along with the board.
