Incorrect unit allocation size. error comes when Tuning the Database

Here iam Using the SQL IDERA tool for checking the Index and performance of the Database, then i found below error, can any one tell what is he talking about.

Incorrect unit allocation size. Drive C: has a queue length average of 7.26. This drive is also responsible for writing the transaction logs sequentially and performing the read/write of SQL Server pages which is typically random

This results in latency currently measured at 0.0036ms as the head moves between sequential transactional log writing and the random Reading/Writing of SQL Server pages. The unit allocation size has been detected to be 4KB. SQL Server works far more efficiently with unit allocation sizes of 64KB and larger.

Recommendation: It is recommended that for busy databases the Transaction logs reside on a different physical drive than the data files and that a unit allocation size of 64KB or larger be used.