2. High Level Design
ext4 allocates storage space in units of “blocks”. A block is a group of sectors between 1KiB and 64KiB, and the number of sectors must be an integral power of 2. Blocks are in turn grouped into larger units called block groups. Block size is specified at
ext4
ext4 ; 16-256 TiB (for 4-64 KiB block size) · 4 billion (specified at filesystem creation time) · 255 bytes (fewer for multibyte character encodings such as ...
EXT4 for very large (>1GB) files
At the moment, the default size of a block is 4KiB, which is a commonly supported page size on most MMU-capable hardware. This is fortunate, as ...
ext4 block size
So it appears to me that the maximum block size that you can define is 4096 KB.