What Is The Maximum USN In Active Directory? Posted on by Webmaster IT Support Forum › Forums › Active Directory › General Discussion › What Is The Maximum USN In Active Directory? Tagged: Update Sequence Number This topic contains 0 replies, has 1 voice, and was last updated by Webmaster 4 years, 11 months ago. Author Posts August 1, 2014 at 11:55 am #615 WebmasterKeymaster Active Directory increments the USN each time a change is made in AD until it reaches the maximum USN. As the USB is stored as a 64 bit number made of 8 bytes, the maximum USN in AD is: 9,223,372,036,854,775,806 That’s 2 to the power of 64 minus 1. This means that if you had 100,000,000 changes every second in Active Directory, your USN would reach the maximum number in year 31,241. Moral of the story: You don’t need to worry about the maximum USN, Active Directory isn’t going to run out of numbers any time soon. Author Posts You must be logged in to reply to this topic.