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PCIe M.2 SSD on FireFly RK339 Findings
Posted at 5/23/2018 05:31:04
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Replies：9
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Last edited by rpk.firefly In 5/23/2018 05:33 Editor
Well I didn't hear back on the forum or from the sales dept. at FireFly.
I did however find the following post over on the Armbian forums by a rather opionated dude, last September. He seems soured due to the misleading PR FireFly put out (and still use):
If you refer to the Firefly Kickstarter page this is just an insane BS collection. I only know that they use an M.2 B key slot which is able to transport a couple of totally different protocols (see here). M.2 B key can either be used for PCIe 2.x x2 or SATA or USB3 (or maybe it's not 'or' but 'and' instead and the highspeed data lines are different ones allowing more than one such a protocol at the same time). Mentioning this theoretical SATA capability by Firefly marketing is of course misleading since RK3399 has no SATA capabilities and for SATA being usable on the M.2 slot there's missing something: a PCIe SATA controller needing another PCIe lane sitting somewhere on the Firefly around (as usual Kickstarter marketing was successful in fooling a lot of users trying out M.2 SATA which simply can not work on this board).
He goes on a little more, but ends with this:
RK3399 is a great SoC for many use cases (attach displays, attach cameras, attach USB peripherals and do with it for what it's designed for: consuming media) but unless someone provides real performance numbers when trying to combine the SoC with reasonable storage controllers I think it's better to ignore this potential use case here. And 'providing real performance numbers' is IMO not that easy since needing the necessary equipment and skills (experts in embedded area are usually missing)
However, someone replies:
According to the Firefly schematic, the M2-B connector on the top has the 4 PCIe lanes, USB 2.0 and I2C connected
The mPCIe connector on the bottom has only USB 2.0 connected.
The PCIe adapter sits on the upper part of the board, so in theory it has access to the 4 PCIe lanes, but who knows whether they all get used by it.
It sounds like some other board resellers are only utilizing a single lane for their adapters.
I'm glad I didn't bother with the FireFly SATA adapter - I doubt it gets any faster speeds than my Samsung T5 connected via USB 3.0, which seems to average 350 MB/sec read/write.
I still don't know if an M.2 SSD is even able to be used for linuxrootfs (Linux root). It looks like FireFly's Ubuntu .img file doesn't have the capabilities added and you need to build a custom kernel.
I would assume that root=/dev/nvmeXXX would be available to set via a CMDLINE flash, but I haven't heard of anyone actually doing this yet.
It sounds like a total crap-shoot, meaning gamble as to whether it works.
At this point my guess is that if they use 2 lanes, *perhaps* 1000 MB/sec is possible. I'll probably order an adapter anyway and an M.2 SSD and give it a shot.
This post will end up being scraped by google, so anyone researching before purchasing a Fly RK3399 will get a heads up.
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