For a Windows-only photo archive drive, NTFS is the best choice. Photo files don’t need any special file system; they behave like any other files. NTFS is the standard modern Windows format and supports large drives and files reliably.

If you specifically need broad compatibility with other operating systems, exFAT can be useful for external drives, but for Windows use, NTFS is the usual recommendation.

For allocation unit size, the safest choice is the default. With modern hard drives, using a larger cluster size is unlikely to give a meaningful performance benefit for storing RAW and JPEG files. Larger clusters can slightly reduce overhead for big files, but the real-world difference is usually negligible.

So the practical recommendation is:

• use NTFS
• leave allocation unit size at default

If you later decide the drive must move regularly between Windows, macOS, or Linux systems, then exFAT may be worth considering instead.