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Today my Synology NAS's OS (DSM) told me that I have a degraded volume. The advice on their site is to replace the failed drive. I've gone ahead and bought the same drive model and capacity, and it has arrived.

However, I'm struggling to know which drive has failed. It may be my lack of HDD knowledge, but the two diagnostic screens in the DSM Storage Manager panel seem to conflict somewhat.

See these screenshots of Storage Pool and HDD/SSD tabs in the Storage Manager:

Storage Manager screenshots

Although the Storage Pool tab seems to suggest that Disk 2 is degraded, the Disk 2 status is "Normal" and Disk 1 is "Initialized" in the HDD/SSD tab.

According to the instructions on the Synology website:

The status of the drive for replacement must be Initialized or Not Initialized.

Perhaps the GUI is the wrong thing to show here, but if anyone could provide any more insight as to which of my disks needs replacing that would be great. Time is of the essence as I'm on RAID 1 with only two drives.

Thanks in advance.

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So it turns out the "Disk Info" listed in the Storage Pool tab are the disks currently contributing to the storage pool, not the disks with issues. The absence of Disk 1 here is the telling sign that Disk 1 is the HDD with the hardware failure, which would corroborate with the HDD/SSD tab's information.

From Synology's support response:

Both screenshots show that Disk 2 is part of the Storage Pool.

In the left screenshot, Disk 1 is missing and this means that it is not in the Storage Pool.

You may have noticed when adding a new HDD, they show up in three different states inside Storage Manager:

  • Not Initialised = No system partition, HDD not used in a volume.
  • Initialised = System partition correct, HDD not used in a volume.
  • Normal = System partition correct, HDD used in a volume.

As Disk 2 is normal, this indicates that it is in a Volume.

Where as Disk 1 is Initialised, so it means that it is not in a volume.

I have swapped out Disk 1 for a new drive, repaired the storage pool and the system is healthy again.

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