I am looking at getting a massive SD card for when my Librem 5 arrives, to have a lot more storage than my current phone offers. Which SD card capabilities does the Librem 5 support? I would like to ensure I get one with the optimal speed and capabilities.
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The spec says that it supports microSD cards “up to 2TB”.
In the schematics, it lists the TE Connectivity 2290741-1 card slot and the Microchip USB2642 card controller, that supports Secure Digital (SD, FAT16 up to 2GB), SD High Capacity (SDHC, FAT32, 4-32 GB), and SD Extended Capacity (SDXC, exFAT, 64GB - 2TB) cards.
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The card controller is using USB 2.0, which has a bus speed of 60 MB/s, but USB 2.0 is half-duplex, so you probably are going to see max read speeds at 30-40 MB/s. The UHS-III spec allows cards up to 624 MB/s, but you aren’t going to be able to use all that speed. You are wasting your money if you buy anything above a UHS-I card.
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Are there even any UHS-III cards on the market? I did a search to see what kind of speeds they were actually able to achieve and the highest UHS rating I was able to find was UHS-II, and that was with a brand I’d never heard of before so that rating is doubtful. All of the reputable brands I could find were only UHS-I.
Yes, it has taken a while for the UHS-II cards to come. Some of the UHS-I cards claim 104 MB/s whereas others claim 50 MB/s. Either way, both are faster than the Librem 5 will be able to handle with a USB 2.0 interface.
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yes. as a general rule it helps to be aware of what the bottleneck is so you don’t EXPECT or INVEST more than what you are currently limited at …
by the way for users that will connect to 1gb/s ethernet that will be a max of 120MB/s in very few cases … what most people tend to get with gigabit DSL ethernet is about 700-800 mb/s if you are lucky and live in a good area where fiber is nearby.
most people end up somewhere in the ball-park of 300-600 mb/s so that is very close to the 480mb/s of the usb2.0.
not a bad place to be in.
First of all, yes, so combine those two answers to work out how long it will take to fill a “massive” SD card. 
Secondly, technically no. You may populate the SD card on another computer and then move it in to the Librem 5. So it could make sense to have a card with much faster write speeds than the L5 is capable of, providing that it is still compatible with the L5.
This is not a hypothetical example. I will probably sync a copy of my music collection from my existing (non-mobile) infrastructure onto an SD card for use in my L5. There is the fast way of doing that and there is the slow way of doing that.
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duh. but that implies that people have access to a second machine that CAN take advantage of the said sd card speed. for users that ONLY have the L5 and nothing else or can’t be bothered to touch another machine then …
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Why Purism used 2.0 usb controller instead of 3.x??
We ran out of 3.0 controllers (if my memory serves me right).
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Sorry I don’t understand, do you mean was set to use 3.x but used 2.0 because finished/unable to find 3.x?
The i.MX8 SoC has a limited number of USB controllers in hardware, and some of them are USB 3.0, while others are USB 2.0.
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Thank you so much for your answer, Dorota. So, please, where I can find tech specs about sdcard to buy?
Is UHS-I 3 30 MB/s (200x) 50-104 Mb/s good for L5? Is it the top allowed for 2.0?
That depends on what you need the card for. I don’t think the SD controller can go as fast as 100Mb/s. UHS-I is the maximum supported.
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So “microSDHC/microSDXC UHS-3 card” in purism shop is too much for L5 I suppose.
https://shop.puri.sm/shop/sd-memory-card/
(Although is into category accessories phone 
)
It’s not “too much” in the sense that the phone will work with UHS-3 cards too, and the phone will benefit from all the storage available on it.
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@velano, see the community FAQ: https://source.puri.sm/Librem5/community-wiki/-/wikis/Frequently-Asked-Questions#214-what-kind-of-microsd-cards-does-the-librem-5-support
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I checked the data sheet for the i.MX8MQ and all the USB controllers support both 2.0 and 3.0, but the issue is that there are only 2 of them. In the schematics, one is used for the USB-C port and the other is used for everything else (MicroSD, WiFi/BT, cellular modem and test points). I assume that the reason why the designers selected the USB2642, which only supports USB 2.0, is because the WiFi/BT and cellular modem only support USB 2.0, so the bus can’t operate at USB 3.0 speeds.
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Oh, that might be it. Now I remember which controllers we ran out of - the MMC/SD controllers. One went to the eMMC storage, the other to the WiFi module.
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FYI looking at an actual Librem 5, in software, I would say that the following are on the other USB
- uSD card reader
- modem card
- (maybe) Bluetooth
not WiFi.
If Bluetooth is on there then it certainly can’t use USB 3.0 speeds anyway.