How to format an SD card to fat32 with custom Allocation Block Size

apple.stackexchange https://apple.stackexchange.com/questions/260083

  •  07-04-2021
  •  | 
  •  

Question

I would like to format an SD card to fat32 with 64kb Block Size. Disk utility seems to do use 32kb by default and there is no option to change this. Is there a terminal command to do what I want to do?

Was it helpful?

Solution

To format a disk with custom (FAT) allocation block sizes use the -c option with e.g. sudo newfs_msdos -F 12|16|32 diskXsY. -F is the FAT type (usually FAT32 here).

First get the disk identifier with diskutil list and the block size of the disk with diskutil info diskYsX | grep "Device Block Size".

To get the -c factor divide the wanted allocation block size by the device block size: e.g. 65536/4096 = 16. Acceptable values are powers of 2 in the range 1 through 128.

Assuming the device block size is 512 Bytes in your case, the factor is 65536/512 = 128 and the resulting command is:

diskutil umount disXsY
sudo newfs_msdos -F 32 -c 128 diskXsY

An additional -v name option will also add a name for the volume.

Licensed under: CC-BY-SA with attribution
Not affiliated with apple.stackexchange
scroll top