Will Whang’s RPI5-SDexpress-Hat is a small HAT+ for the Raspberry Pi 5, adding a microSD Express card slot for ultrafast storage, an eject button, and two Qwiic connectors, probably because there was still some spare space on the board…
As a reminder, microSD Express cards can deliver SSD performance thanks to the use of of PCIe interface and NVMe commands. The standard was first introduced in 2019, and even earlier (2018) for full-size SD cards, but manufacturers have not exactly rushed to release compatible hardware. A major change this year is the launch of the Nintendo Switch 2 portable game console, one of the first mass market devices with a microSD Express slot, and this was partially why Will created the microSD Express HAT+ for the Raspberry Pi 5.
RPI5-SDexpress-Hat board specifications:
- MCU – WCH CH32V003 RISC-V microcontroller for hotplugging and unmount
- Host interface – PCIe Gen3 x1 FFC connector
- Expansion – 2x Qwiic connectors
- Misc – Eject button, Power LEDs, Mounted LED
- Power Management
- 5V supply via 40-pin GPIO header (6-pin header used)
- 1.8V/3.3V fixed output
- LP5907 voltage
- PAM2306 step-down DC convertor for 1.8V voltage
- Dimensions – Small
The good news is that it just works:
Here are some storage benchmarks using PiBenchmarks.com with the Raspberry Pi 5 configured to use PCIe Gen3 x1:
|
1 2 3 4 5 6 7 8 9 10 |
Category Test Result HDParm Disk Read 631.68 MB/sec HDParm Cached Disk Read 699.12 MB/sec DD Disk Write 169 MB/s FIO 4k random read 48761 IOPS (195047 KB/s) FIO 4k random write 26290 IOPS (105160 KB/s) IOZone 4k read 22803 KB/s IOZone 4k write 137502 KB/s IOZone 4k random read 31366 KB/s IOZone 4k random write 178701 KB/s |
The read speed is indeed better than a typical microSD card (630MB/s+), but the sustained write speed is closer to a high-end traditional Class A1/A2 microSD card at under 200 MB/s. Random I/IOs are much better, too.
You may wonder why a microcontroller is needed here. As one reader explained in our article about a microSD Express to M.2 NVMe SSD for the Nintendo Switch 2, some logic is required (update: maybe not):
It will not work without a proper SD handshake and CMD8 command response with PCIe flags as SD host controller needs to enable and reset PCIe side for this to work…
The design is fully open-source with KiCad schematics and BoM available on GitHub, where you’ll also find the firmware binary for the STM8S CH32V003 MCU, but no source code. The project is based on Will’s earlier RPi5-CFE-Hat CFexpress Card hat for Raspberry Pi 5, whose firmware’s source code is available, so it’s probably just a matter of time.
Sadly, having a microSD Express card slot on the Raspberry Pi 5 does not make a lot of sense at this point due to the cost of MicroSD Express card. An M.2 NVMe SSD is cheaper, and so is a CFexpress Type B card. For reference, the Samsung 256GB microSD Express card used in the demo sells for $59.99 on Amazon, while a similar SSD goes for about $25, and an M.2 SSD in a CFExpress Type B card is also slightly cheaper.
For those reasons, Will will not manufacture the HAT, but the design is released under a permissive MIT license, so anybody could manufacture it if needed. Maybe a microSD Express slot will make sense in a future Raspberry Pi 6, as prices come down.
Update: The article was updated to change STM8S (as in the PDF schematics) to CH32V002 as reported on X, and a few other details.
Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.
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Just as a slight counterpoint, I picked up a Walmart branded Onn 512gb for our switch 2 for about $60 a couple of months ago.
Yes and on an exposed board maybe you think of an SSD as “removable storage” but in a consumer product it’s really a “fixed disk. Some of this pricing is a question of packaging and convenience.
The belated Switch 2 miracle made microSD express real. I wonder what it will take to get microSDUC support.
Why do you want QLC NAND in your microSD cards?
I am thinking about this for industrial prepress and commercial photography workflows, or maybe the card reader at your drug store or shipping center consumer printing service.
There’s also a thought about other unspecified sneakernet workflows, like infosec contexts, compartmentalized information facilities.
Fast reads.
Keep in mind that these cards run hot during sustained read/writes, so a heatsink on top of the card reader might not be a bad idea if you want better sustained performance during long read/writes.
That is not the case when I test the board – I basically did a long read/write stress test with and without fan to see if there is any thermal throttling but there is none.
Nothing to do with the board, but maybe they’ve fixed the cards, as the early ones ran really hot.
This is specifically why I mentioned the cards, not the board.
Data recovery services.
I’ve also had the misfortune of buying sdcards online in Southeast Asia with too good to be true pricing, counterfeit, faulty storage, addressable space much smaller than advertised. Probably being sold for resale to tourists. Would but nice to have an app to quickly identify that.
You’re aware all memory cards are made in Asia right?
That you got scammed by some dodgy seller that sold you knock-off crap, doesn’t mean you should trash the rest of Asia.
Hat makes it not very different in size than m.2280 stick, in fact the latter can be more compact. However going forward all those discrete chips integrated is what I imagine, and of course putting these things thru test of time, water, and tear. Over time price difference should narrow, but again we don’t have good estimates how long all that takes. Ssd was supposed to obsolete hard drives 7 years ago, clearly not yet.
Another, much smaller design for a microSD Express adapter (not HAT): https://www.cnx-software.com/2025/08/01/microsd-express-pi-adapter-is-an-ultra-small-microsd-express-adapter-for-the-raspberry-pi-5/