By Alexander's and Arabians' and Tatars' attacks to Iran, they destroyed each documents and books they can, But Iranians didn't destroy the documents savagely such as Greek's and Romans' attacks. Because of not destroying these information by Iranians, Today you can know the history that Greek and Romance historian said.
Iranians are not only Persian. Iran is a country with a people including Kurd, Azari, Persian, Sistani, Ghilaki, Caspian, Balouch and etc.
You should know that most of your knowledge about Iran is not true, these information was made by media and the books from Greek and Roman historian like Herodotus. Nowadays, new historical document have been discovered that show the information about Iran told by Herodotus is incorrect.
All of the diaries in Iran are not made by Iranian people. The Islamic Republic government of Iran made the recent happens not all of Iranians. You should know the government of Iran don't allow anybody in Iran to make a movie about Cyrus the great or Zarathushtra. They want to have Arabian Islamic identity not Iranian.
Please go and find the new result of history which are in other countries' universities (like university of Michigan). If these documents were in Iran, They would be destroyed by Islamic Republic government of Iran.
If you want to know the reality please listen to Iranian historians and culture, It can help you that the history resources you know is correct or incorrect.