Disk is showing high Reallocated Sector Count and ATA Error Count
I have two ST31000340NS disks which have been in my Duo for many years, after a couple of annoying power outages (before I had an UPS) one of them started to show a Reallocated Sector Count, and also an ATA Error Count. Over the years and at least one full format later it's showing 138 Reallocated Sector Count and 979 ATA Error Count. The other disk is showing 2 Reallocated Sector Count and 6 ATA Error Count (possibly caused by the same power outages, though one disk was always worse affected than the other).
Clearly disk one is suffering, but is it necessarily something I should worry about, are both disks just ready for the scrap heap or can the errors be worked around? Will there be data loss or corruption that the Duo can't detect or correct? This is currently on backup duty, it's a mirror and backup location of an external drive I use primarily for video editing.
I am planning to replace both disks with 2TB HGST HUS724020ALA640 (which I believe is simply a newer version of the UltraStars on the compatibility list), but I feel it would be a shame to throw away the two 1TB disks if they can still be used in some fashion.
I have two ST31000340NS disks which have been in my Duo for many years, after a couple of annoying power outages (before I had an UPS) one of them started to show a Reallocated Sector Count, and also an ATA Error Count. Over the years and at least one full format later it's showing 138 Reallocated Sector Count and 979 ATA Error Count. The other disk is showing 2 Reallocated Sector Count and 6 ATA Error Count (possibly caused by the same power outages, though one disk was always worse affected than the other).
Clearly disk one is suffering, but is it necessarily something I should worry about,
I'd certainly replace the one with 138 reallocated sectors. In my experience, attempting to "repair" or spare the bad sectors doesn't end well. Once disks start to fail, they just get worse. You're better off replacing at least that one. The other one might be ok, but you should keep an eye on it if you want to keep it in service.
The HCL for the legacy NAS hasn't been updated in several years, and almost all of the drive models there are out of production. It's best to ignore it, and just get a CMR NAS-purposed drive. You do need to be careful when using desktop drives, since many of them are now using SMR, which is not a good choice for NAS.
If you decide to go with 2 TB, then I'd suggest going with WD20EFRX or ST2000VN004. While they aren't 7200 rpm, users here have found them reliable - and the Duo isn't really fast enough to take advantage of 7200 rpm drives anyway. (Avoid the WD20EFAX, as it is SMR). Reasonable 1 TB models are the WD10EFRX or the ST1000VN002.
HGST was acquired by Western Digital back in 2012. While WD still does use the UltraStar brand, none of the currently shipping Ultrastars are compatible with your NAS - they are too large, and many of them are SAS drives. The HUS724020ALA640 was certainly a reliable drive - but it isn't manufactured now, so anything you purchase would be older inventory.
Re: Disk is showing high Reallocated Sector Count and ATA Error Count
Thank you for your reply, most helpful.
Note that I already have the 2TB HGST drives, they are on their way out of my NV+ (currently synching in a pair of 3TB disks), one has 2 Reallocated Sector Count but no ATA Errors, so I'm saying that's still good.
Re: Disk is showing high Reallocated Sector Count and ATA Error Count
A reallocated sector is in the word - reallocated. So, the HDD detected and issue with a sector and moved the data to another area on the drive and marked the original sector as bad. This is a better outcome than an uncorrectable sector error where the data in sector is lost and can't be recovered (though through RAID parity, the filesystem will recover the file(s)).
I couple of reallocated sectors isn't necessarily a sign of imminent failure of the drive in the near future, so if your drive has like 2 reallocated sectors errors now, I would simply keep an eye on it and if it start to increase - replace it ASAP.
