My NAS Storage Pool Is Degraded: What Should I Do First?

These actions can lose data. Do none of them until a copy exists elsewhere:

• Do not remove a second drive while the pool is degraded. UGREEN says that if another drive develops bad sectors or fails during this period, all data may be permanently lost, and says never to remove multiple drives at once.
• In a degraded RAID 1, UGREEN says the remaining drive holds all the data and there is no fault tolerance left. Disabling it would lose everything.
• Asustor says replacing several drives at once, or replacing a drive while the NAS is synchronizing, causes data loss.
• Do not guess which drive failed. Synology says to confirm the defective drive on the HDD/SSD page, and TerraMaster says to identify it from Message Notifications.
• The replacement drive is wiped. Synology says all existing data on it is erased, and TrueNAS wipes it as part of the process. Never use a disk that holds data you need.
• In TrueNAS, the Force option overrides the safety check and erases any data on the selected disk. Do not tick it unless you are sure it is the right disk.
• TrueNAS does not recommend leaving a failed disk online unless you know the exact condition of that disk.
• Synology says drives not on its compatibility list may affect system stability and result in data loss.
• If Synology shows the pool as Crashed instead of Degraded, Synology says you can no longer repair it yourself. The steps on this page are not for that case.