The HGST Ultrastar drives I bought weren't for a NAS. They are used as storage drives in a desktop computer while one is used as an external drive for backup purposes. They power down when not used & are quiet when in use. A few years ago I bought a Western Digital Black drive & it vibrates & gets hot & doesn't power down. I was glad to retire it. I've never had a HGST Ultrastar drive develop a bad sector despite many years of daily use. I did buy an Ultrastar drives once which was faulty despite being new & it was replaced under warranty.