QNAP and broken disks

This case highlights one quirk in QNAPs,

TS-212 disk2 in raid 1 replaced after failure won’t rebuild. ISSUE is that the second drive in raid 1 array failed and in degraded mode. Second drive is in an unmounted state and will not mount on it’s own or format.

original drives where:

disk1: Seagate ST3000DM001-1CH1CC24 – 2794.52GB

disk2: Seagate ST3000DM001-1CH1CC24 – 2794.52GB

disk2 failed so swapped disk2 for: WDC WD3000F9YZ-09N2001.0 – 2794.52GB

I tried the following commands [whatever]. always gets stuck saying

disk 2 is busy so it can’t add it to the raid 1 array.

Although the model is identified as TS-212, the problem affects many if not all QNAP models. If there is a disk  with bad sectors, the unit will sort of stall and will be not able to read any of the disks in it, or will read it very slowly, so that waiting for even simple operation to complete may be not worth it. Disk models, Seagate whatever or WD, are a red herring – QNAP may behave the same with a disk of any vendor if the disk has bad blocks on it.

The solution in this case is to shut down QNAP, remove disks one-by-one and clone them to a new disks, then re-insert disks into the QNAP and power it back on. Once there are no bad sectors on the disks, the recoveries/rebuilds usually proceed on their merry way.

I do not know the exact reason why this happens, but it may well be something associated with either the QNAP chipset or some quirk of the firmware.