The simple solution is to reformat in exFAT with an allocation unit size of 128k or less. What allocation size should I use for exFAT? What is the allocation unit size for a 64GB USB?Īccording to Hitachi, the recommended cluster size for a 16GB FAT32 partition is 4KB, the recommended cluster size for a 64GB FAT32 partition is 16KB, the recommended cluster size for a 128GB FAT32 partition is 32KB and the recommended cluster size for a 256GB partition is 64KB. This covers many scenarios, especially when working with many small-sized files. If you are a standard Windows user then the proposed allocation unit size of 4096 bytes sounds good. Windows 10, by default, when choosing to format a USB flash drive, propose as the Allocation Unit Size the value of 4096 bytes. What allocation unit size should I use for flash drive?