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I know that on a rooted phone, it's reasonably normal to create a small ext4 partition for App2SD to use, but I'm not asking about that case: I have a non-rooted HTC Desire running Froyo, and I'd like to format the whole of my SD card as ext4 instead of FAT. I'm aware that this will mean that Windows PCs won't be able to use the card, but all my PCs run Linux so they should be fine. Will the phone be able to access and use the card in this case?

Izzy
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Andrew Aylett
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5 Answers5

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I actually had my sdcard on ext4 and got it mounted permanent at boot time (I have root on my phone).

The biggest problem was that the apps don’t expect permission checking on /sdcard, but extX enforces this (no mount option around this). So if one app stores e.g. some audio there and calls another subcomponent to play it, it fails.

The same is true for photos (camera shots them, some previewer might want to access them).

You can manually fix this, but you have to run after every new file created... There would be an nice real solution to this, but it requires system modification: let the apps run with umask(002) instead of 022. Android is UPG (User Private Groups), so there is no big harm in doing so. – Now the apps could choose if they want to expose files to others by setting the group to “sdcard“, or not. This would also add to an enforced separation where the apps want it.

Robert Siemer
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    Get fixed permissions using FUSE or sdcardfs: https://android.stackexchange.com/a/217936/218526. But this answer isn't for non-rooted phone. – Irfan Latif Jan 04 '20 at 00:40
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ext4 should be supported if you have an upgrade to 2.3 or 3.0 Android (I see that your post is from just before the 2.3 & 3.0 releases...).

...and when btrFS is added to Android, it has a nice mount-option ",ssd" with wear-levelling etc that ext4 doesn't have... and more speed than ext4 now, esp if you use ",compress=lzo" OR ",space_cache" in fstab (but don't use compression WITH the space_cache option, only use 1 or the other or else it slows to a crawl in some benchmarks) -- and that speed comes despite btrFS checksumming of all data (not only of the journals, as ext4 does). :-)

Goldfanger
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    Just an update from 2017: I think this is really only valid if you have a rooted device, unfortunately. – Jesse Adelman Jul 24 '17 at 18:33
  • Just an update from 2021, still not working on Android 10. I also tried an XFS formatted thumbdrive, still nothing. – 15 Volts Mar 16 '21 at 06:58
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It appears that the answer is "no" :(. I was asking because I have a new card to go in the phone, so I thought I'd just try it -- it didn't work. When I ask the phone to mount its card, it goes straight to saying "SD card safe to remove."

Oh well.

Andrew Aylett
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Short answer: no.

Although on Android 5 cat /proc/filesystems shows that ext4 is supported it seems that only FAT32 and exFAT (FAT64) are supported on non-rooted devices. I've tried mounting 64GB micro SD card as exFAT without any success.

Using fdisk you can format your card to FAT32 (files over 4GB are not supported):

$ fdisk -H 224 -S 56 /dev/mmcblk0

  • d delete previous partition
  • n new partition, then select primary one p and default sector start e.g to 2048
  • t set c for FAT32
  • (here you can save few sectors by going to expert mode x and moving begin of partition b)
  • w write changes

Then format to FAT32, using your number of reserved sectors (2048)

$ mkfs.vfat -F 32 -s 32 -R 2048 -v /dev/mmcblk0p1

  • -F 32 for FAT32
  • -s 32 cluster size expressed as sectors, so 32 x 512 bytes = 16KB clusters
  • -R 2048 number of reserved sectors

This way 64GB card can be mounted using FAT32, I didn't mange to find any working formatting for exFAT or ext4.

Tombart
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I tried LineageOS 14.1(android 7.1.2), it support sdcard(tf-card) formatted in ext4. Though it format sdcard to vfat defaultly, if you don't make any patch. The easiest way is to format the sdcard with ext4 using a external usb-sdcard-adapter, then insert the sdcard into phone with LineageOS installed.

neoedmund
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