Try one or all of the methods below to resolve this error.
If there are no drives currently installed on your Synology device, install at least one 3.5" or 2.5" compatible drive before installing DSM. Refer to your device’s Hardware Installation Guide for details.
If your Synology NAS has 2 or more bays:
1. Power off your Synology NAS.
2. Switch the order of the drives or first insert only one drive into a slot.
3. Power on your Synology NAS and try installing DSM again to determine if the problem is caused by the drive or the slot.
If DSM was already installed on the drives and you have been using the drives for some time, but Synology Assistant or Web Assistant suddenly displays Not installed, this indicates that your device cannot recognize the drives. In this case, abort the installation, shut down your device, and refer to the relevant instructions. You can also connect the drives to your computer and use the following diagnostic tools to check drive health:
- Western Digital (WD): Lifeguard
- Seagate: Seatools
If the issue is that installed drives do not appear in Storage Manager:
- Make sure the drives are listed on the Synology Products Compatibility List.
- If there are empty drive slots, insert the drives into these slots to check if they are displayed in Storage Manager.
- If there are no empty drive slots, try connecting the drives to a computer to see if they work.
- If there are no empty drive slots and you do not have a computer available, shut down your system and take out all the installed drives. Insert the drives which were previously missing from Storage Manager into different slots. Restart your device and open Synology Assistant to see its status:
- Not installed: the drives still cannot be found in other slots; the drives themselves may be faulty. Try using a different drive.
- Ready: the drives are successfully identified in different slots; the issue likely lies with the previous drive slots.
If you can log into DSM, run the built-in S.M.A.R.T. test to scan the drives.
If the problem remains unresolved, contact Synology Technical Support for help.
Sources used: [9], [10], [11], [4]