Disk failure can occur without any warning signs even when the hard disks have been tested normal by S.M.A.R.T. test. According to a study published by Google Research, after the first scan error, drives are 39 times more likely to fail within 60 days. It is important to always back up your data as a precaution.
Desktop class hard drives are designed for balanced performance and reliability for everyday computing, while enterprise class hard drives are designed to deliver higher performance standards suitable for 24x7 mission critical business applications. Hard drive manufacturers strongly recommend installing enterprise class hard drives for the RAID environment regarding to these reasons. Please choose the hard drive that fits your needs.
To ensure full compatibility, always choose hard drives as compatible below. Users have reported here for other hard drive models which are compatible with their Synology DiskStation, you may refer it at your own risk. Or suggest Synology to test a specific hard drive model by submitting a hard drive suggestion form.