[One (M8) Original Android Development] CutGlass:
MicroSD 64 Gb+ testing.

Over-exerted myself with this one.

From the previous experiment I have the Toshiba 64Gb card formatted by lineageOS 31st Jan as FAT32, so decided to test it "as is" in case there was a formatting on the device issue.

Taking a 1.6Gb file from a TWRP backup called data.ext4.win000 it's md5sum was b358e8146d915773b6ab14720838c918. (Handily confirmed by an md5 file in the twrp backup itself :fingers-crossed:

Put it on the 64 Gb card using a USB adaptor tested it again using md5sum form a bash terminal and was identical.

Moved to a MacBook out of curiosity to see if it handled filesystems differently (possibly the extra byte or different interpretation of how many blocks were used) again the md5 was identical (Note. Mac terminal uses md5 not md5sum.)

Installed LOS 31st Jan with factory reset on device, with the same card in checked through TWRP's terminal and MD5 was identical before and after installation, also took a fdisk -l to confirm the size of sd card and how it was originally formatted.

Using an ADB shell before booting into LOS, confirmed that md5sum was also identical.

So we have linux, macOS, TWRP and ADB all confirming the md5.

Then booting into LOS and using the play store to install a terminal emulator (Termux) and the free busybox (the one with the cardboard box and # sign on it does the job and is free, second on the list in play store on a search for "busybox"), (I realised I could not us su - even after having turned it on in developer options because I'd forgotten the addon_su zip file). After correcting that, using the same 64Gb card, confirmed that the md5 was the same "on device" using only terminal and the command line "on device".

The format from the previous test named this microSD card FF86-1B06 visible in the text file.

******

Using the Android wizard by long pressing on the card in settings > storage, it was formatted as portable storage and then the 1.6Gb file copied from a PC (Linux) by plugging it in and drag and drop using MTP

******

Turning on an ADB shell and turning off MTP (because I was sick of not having a decent terminal emulator at this point and I wanted a quick check with a TAB button, the SD card was renamed to F611-12F8 by the format and the file transferred was md5 identical again.

Then using the terminal emulator (remembering storage su - which brings up the permissions dialog) I confirmed that the md5sum was identical to all the previous ones on device, did an fdisk -l /dev/block/mmcblk1 to confirm the SD card appears formatted the same (FAT32 one bigger than recommended partition).

So this slow toshiba card works at 64Gb on LOS 31st Jan HTC M8, I'll dig out the packaging for a model number.

Notes.

The Lexar 64GB I use was originally Marshmallow on some Motorola G before going to lollipop and F2FS. I don't expect anyone to do a test like this my main "issue" was that my daily driver uses f2fs on the SD card and the reports were that large files were not working on 64Gb+ cards so my device had to be put back to recovery and slots pried open, if you already have portable storage for the sd card then just test it out much quicker and a simple yeas or no would be sufficient.

To create the attached file on the command line I used md5sum /storage/F611-12F8/data.ext4.win000 >> md5s.txt and for all the data including echo "" and putting in the titles (were cleaned up a bit), so the card was a) being used read write, b) can anyone recommend a decent terminal emulator for Android I tried two during this, one "Terminal Emulator" claimed the Vol keys would act as function keys and cursor keys for would be very nice, because it is a royal pain in the butt to type out /storage/F611-12F8/data.ext4.win000 once, let alone twice to repipe it to the text file when you are used to 20+ years of TAB autocompletion *rant over*.