BTW. In case someone doesn’t care about WiFi and Bluetooth but cares about fast access to SD card - you could put such card in place of a WiFi module and achieve up to 104MB/s 
(perhaps even more, but can’t tell from memory, would have to check the specs)
3 Likes
Speaking for myself only, I do care about WiFi (and sometimes Bluetooth).
Maybe someone can come up with a combo card that does WiFi+BT and gives some faster local SD storage. No idea whether this is actually possible within SD functionality.
(I understand that while I am syncing the local storage via WiFi with my server, I may well halve the available bandwidth to disk but that would still be way better than now.)
1 Like
If such “combo card” used USB instead of SDIO for WiFi+BT and could fit it all into a M.2 card then it would be actually trivial - though now your WiFi would be limited by USB 2.0 speeds and power management gets slightly complicated, which may or may not be a problem depending on your use case
2 Likes
Or the other way round: keep the WiFi+BT on SDIO and use USB for the storage interface? That would still get way better bandwidth into the µSD card.
And, yes, either way, fitting it all into the M.2 card form factor is a challenge.
Since we are just blueskying … there are two approaches for the storage: µSD card slot (comparable to now - but probably needs more space) and fixed storage - with the obvious trade-offs.
1 Like
Since we’re going this far off with what ifs, have you seen those little cases that attach on the back of the phone and have a small (physical size) NVMe disc that is connected via usb-c? Search “phone nvme disc case”. Made for those phones that don’t have a card reader at all but still usable if you want a big fast local storage. Some even have a second usb-c to charge while it’s attached.
2 Likes
Way better?
Again, while the maximum transfer rate of USB2.0 is 60MB, the effective throughput is going to only be 30MB/s to 35MB/s (theoretical max throughput is 53MB/s, but …). That’s twice the current rates of the sdcard interface, but it’s still not much. i.e. USB2.0 is a limiting factor.
For fun you could try your USB3.0 dongle with your UHS-I card plugged into the USB2.0 port of your computer. I’ve got a guess: You’ll get around 20MB/s writes and 40MB/s reads.
1 Like
Or you could read the OP for the actual figures. (I realise that I added that several days ago but after you read the OP. So, yes, your guesses are pretty good.)
So for read speeds we are looking at almost 4x faster. Not to be sneezed at!
That’s still not really where I would like it to be but the important point in this now rather theoretical discussion is what could be achieved without changing the main board i.e. what could theoretically be achieved with a Librem 5v1 i.e. accepting that once we do hit the USB 2.0 limits that’s what we are stuck with.
And there’s the original (hypothetical) option that was proposed in this topic (storage on SD interface, WiFi+BT on USB interface) where the WiFi would hit the USB 2.0 limits but the storage would then go much higher speed. Whether a customer would choose that would typically depend on the speed of the home internet.
1 Like
Completely agree!
It would be nice to swap buses for SD and WiFi between together… May be in the next batch?
1 Like
I didn’t recall that test. Sorry. I did cheat however [with my own cheap dongle and an old card UHS-I that got 42MB/s-43MB/s read and variously 15.0MB/s, 14.1MB/s, and 5MB/s (with USB transmission errors) writes on a USB2.0 port. I didn’t want to mention because the dongle is cheap, the card is old, and it only gave 16.4MB/s writes and 82MB/s Reads on a USB3.0 port … which was significantly slower than your write speeds].
2 Likes
That would be a different option again - but of course not achievable without a change to the main board - which is why dos and I were talking about an M.2 card that replaces the current WiFi card and which offers both SD storage and WiFi and which already has both SD and USB interfaces available to it (hence can use them in two different alternative configurations).
2 Likes