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Hey just updated to LOS18.1 and this approach seem not to work anymore :-/
In short the commands:
adb shell cat /proc/mounts | grep storage
#--> get ID if the card here 52D3-1E21
adb shell cat /proc/mounts | grep 52D3-1E21
# umount all mountpoints
adb shell umount <mountpoint>
# format as ext4
adb shell mkfs.ext4 /dev/block/mmcblk1p1
# remount
adb shell mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1 /mnt/media_rw/52D3-1E21
## visible again but as under 17.1 only 1GB size
## -> reboot
## Shows "Issue with <SD card name>"
## no way to fix this except formating again
Any suggestions?
@Ingo vielleicht hier mal noch cross-posten: Filesystem: it's possible ext4 on sd-card? - Using / e / - /e/ community
vielleicht hat da ja noch einer eine Idee.
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Btw. (a bit off topic, but): My personal reason, why I did this, was/is that there are apps like Signal which grew a lot over the time and so also the backups of Signal are bigger than 4GB. So I cannot safe the backup (and there are 2 files - no option right now do change this) on the external SD, even it is encrypted. 
Looks like that someone developed a way that the backup will be split into 1GB chunks.
Not sure what needs to be done that this will be accepted and done (the PR merged) by the Signal App Devs.
That’s exactly the point where I also need help :). My Signal backup is larger than 4 GiB and I can’t used anything other than FAT32 for the external SDCard :-(.
Singu
Did you guys try to format in exFAT? It’s not officially supported by android, but IIRC it works on the FP2 and doesn’t require all the hacking ext4 needs. And it supports much larger files.
Not yet and I switched to FP4 with CalyxOS.
The FP4 has much more space, so this issue does not exist anymore for now. Even though I think a lot can go to the external SD (downloaded maps, downloaded Spotify songs; anyway encrypted stuff like messenger backups, Neo Backup files, etc.).
@Singulus I also took part of this github dicussion, which would help a lot, at least in regards of the Signal big backup files issue. But it seems to take ages until the Signal devs accept such external PRs. 
introduce chunked backups by Roghetti · Pull Request #11900 · signalapp/Signal-Android · GitHub
If you have a github account, maybe a comment there, that you need that, would help or push this and/or like Roghetti’s posts.
@Alex.A ok, exFAT might be an option, as it seems that I have to re-fomat the external SD for my FP4 anyway (I just moved it from the FP2 to the FP4 and it acts strange and is not read-/writeable for some apps - but potentially it has another problem or is broken in general).
What to you mean that is does not need the hacks? Is it just formating with the PC? Will it be accepted by Android without re-formating?
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AFAIK yes. I can’t find a spare SD card to test now, but if you can, it should.
Hm this would be surprising if this is working, as I wasted a lot of time make ext4 working ^^ (as we can see in this thread). Anyway currently trying with my old FP2 and an older small 32 GB SD Card (I erase and format it with my PC to exFAT) … will report back.
Nope doesn’t work. Android asked for re-formating also with an extFAT SD card.
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Just formatted an old 8GB Sandisk to exFAT via Win11
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Moved to FP3 with A.0016β no query
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Close and open phone, prompted to ‘Set up’ SD card
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Select ‘Use as portable’
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Discovered photo not saved to SD card using default camera app
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Under storage the SD card is seen as ‘disk’ not *SD card and all the ‘Android’ folders have been created.
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Reinsert in PC > still exFAT so clearly the phone can write to the SD card as it has created the folders.
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Transferred video whilst in PC, plays on FP3 fine.
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Can’t use ‘disk’ as storage location using default or Open Camera.
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Can move files manually from FP3 to ‘disk’
Restarting Phone
OK now Open Camera is saving to ‘disk’ 
- Default camera still ignores option to save to SD and reverts to phone. This was a problem earlier and I wonder if there is a regression in the 0016β
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For me this was NOT the case, neither with exFAT nor with F2FS nor with ext4. One FS seemed to be recognized but it couldn’t be accesses as it seems read-only.
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I opened a bug report for LineageOS, which is ignored until now:
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Okay, my bad then, it may have been too long ago if the change (as you mention in your issue @Singulus) is recent.
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Just found this thread:
which points on this one → ✏ List of compatible micro SD / SDXC cards for FP4
I have a 128GB SanDisk Extreme A2. Maybe it is also such a SanDisk SD related problem.
For the record, FP4 here, latest updates. I got me a Kingston Canvas Go! Plus SDCG3 of 256 GB, which came factory-formatted as exFAT. The phone did accept it (“portable” setting) and the default camera didn’t have any problem using it to store pictures.
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Also, for the record, SD cards have a somewhat special formatting and should if possible not be formatted with the usual (Windows/Linux/Apple) tools. You risk problems on the long run.
Fortunately the SD Association offers a free SD card formatting tool (Windows and MacOS only).
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Got a Samsung PRO Plus 256GB U3 A2 V30 Class 10 and it arrived exFAT factory-formated as well. The FP4 with CalyxOS accepts it without any issue as portable storage.
I will not go on researching this, as I shared a lot of details here (with my former FP2 [which the thread is also tagged with] → FP4 now) - and I was out of ideas, but I’m still curious what this “special” should be. At the end exFAT is exFAT, the formatting tools cannot do it differently. There has to be something in the header or so, which makes it special. Also there could be device differences and or newer Android Versions handle all this differently.
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I had problems with my Sandisk 512 GB U1 card with exFat so I ordered a SAMSUNG EVO Plus 512 GB which works fine even after formatting it under Linux.
I wanted to try ext4 first. BTW I do not understand why this is not working for many Android versions and different devices, now. Except for AOSP or LineageOS based systems.
Well, it’s just an educated guess, but I think it has to do with “overprovisioning”, i.e. the fact that flash memory-based disks (SD cards, SSDs) keep a stash of unused memory cells to use when (it’s not “if”, it’s “when”…) one or more memory cells cease to function. Think of it as spares.
I assume the “special” formatting is all about preparing the disk for this, so the firmware can do this without the user even noticing. And that’s the obvious explanation, there might be something else too (write amplification prevention, wear leveling, TRIM, etc.). There are lots of special functions a flash memory based disk requires to be able to work optimally, so I guess exFAT on a SD card is actually just something posing as exFAT to the OS: “Don’t worry, I’m just an exFAT disk, I’m not some monster from out of space”… 
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