About half a year ago my old 1.5TB SATA Green WD HDD tapped me on the shoulder and said: "Hi, very soon you won't be able to read any data from me."
As I have not made my backups regularly, I took this warning seriously and decided to finally realize my old idea of moving from ext4 to ZFS. So, I have bought a 500GB SATA Green WD HDD. Based on its price, I suspected it was refurbished, but I didn't have much choice since the Green WD HDDs were apparently no longer in production, and the 2TB Gold WD HDD was incomparably more expensive. After installing ZFS on it, it turned out that everything works well. So, I decided to buy two other WD HDD of the same model, to set one of them as a ZFS mirror and leave the third WD HDD for the time when one of its twin brothers fails. This time the seller warned me that these WD HDDs are refurbished but assured me that they were refurbished by WD itself. Taking into account that the previous such HDD behaved quite well, I decided to proceed with my purchase. After setting up one of them as a ZFS mirror, I immediately got the problem that if I boot my system with additional HDD connected to my computer, one of these ZFS mirror disks is not detected and the corresponding zpool appears to be degraded. I have realized that it was my fault to use /dev/sdb and /dev/sdc notations when setting up the ZFS mirror because with more disks at the boot time these notations may change. I should have used /dev/disk/by-id/ata-WDC_WD5000* notations instead! Unfortunately, I have not found the way to change these notations other than deleting the whole zpool and re-creating it anew with the notations /dev/disk/by-id/ata-WDC_WD5000*, which took quite a lot of time. Presumably, the problem with detecting my ZFS mirror HDDs should have disappeared after that because now the disks were referred to by their ids but unfortunately it was not the case. When I boot my computer with an additional external HDD attached to the computer via USB, one of my ZFS mirror HDDs is not detected by the system and the corresponding zpool again appears to be degraded until I restart my computer in the usual setup, that is, without any additional HDD attached to it. I have looked into my /dev/disk/by-id/ directory and found out that this happens because one of these ZFS mirror HDDs does not appear in this directory at all! The situation remained the same even after swapping the undetected 500GB WD HDD with the one. So, I wonder if it is a fault of 1) refurbished WD HDDs 2) my almost 20 years old Ultra-Durable Gigabyte motherboard 3) the Linux system itself.
