The unit doesn't recognize some USB storage devices such as USB flash drives and HDDs. Why not?

The connected USB storage device might not be formatted in a supported format. 
The CDJ-3000X supports FAT, FAT32, exFAT, and HFS+.
Please format in one of the above formats.

Note:
* NTFS is not supported.
* When updating the unit's firmware, use a USB storage device formatted in FAT, FAT32 or exFAT.

■ Mac 
USB storage devices used with a Mac might not be recognized due to the following reasons.
・ The CDJ-3000X does not support the GUID Partition Map Mac OS standard format.
・ USB storage devices formatted with Mac Extended format (case-sensitive) might not be recognized correctly.