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> So the NAS drives come with firmware that doesn't do the extreme recovery and instead just returns "read error" and lets the RAID controller rebuild it with
by bityard 7y ago
> So the NAS drives come with firmware that doesn't do the extreme recovery and instead just returns "read error" and lets the RAID controller rebuild it with the parity information.
Hang on a sec. Is this documented somewhere?
I bought a WD Red to plug into my Raspberry Pi which I use as a file server. There's no RAID, just the one disk. I thought I was buying a more energy efficient or bulk-storage-oriented drive.
But if what you say is true, then the "NAS" or "Red" drives should _never_ be used outside of a RAID because robust error correction was removed from them by design. Do I have that right?
- Silhouette 7y agoYes, that's the right idea. NAS/RAID drives have a different error recovery strategy, because the assumption is that they'll be part of a multi-drive arrangement where failing fast (and allowing the containing system to handle recovery) is preferable to avoiding failure if at all possible (but potentially taking a long time and thus causing the containing system to think the drive has stopped functioning properly and fail the whole thing out). I can't point you to any specific documentation off the top of my head, but this is a well-known position that I've seen described explicitly several times. I'm afraid that does mean your choice of a Red for a single-disk system was not ideal. Presumably you keep backups of any valuable data anyway, but if downtime for recovery would be a significant problem for you then you might want to consider replacing that drive with something more suitable for your situation.
- magicalhippo 7y agoIf one uses ZFS, one can instruct ZFS to keep multiple copies of the data. It will try to spread those copies among multiple disks, but in single-disk systems it will just spread the duplicate blocks over that disk. Since ZFS does checksum verification on every read, it has a much better chance of recovering from a few bad sectors. Downside though is that the default RPi installs are 32bit and ZFS was written with 64bit-only in mind, and AFAIK there are still some issues and limitations when running on a 32bit system.
- bityard 7y agoI should hand in my geek card, this feels like something I should have known about. In my defense, though, the HD manufacturers offer little to no information about the _technical_ differences between their drive lines. All of their documentation just says, "designed for X use case". I do have backups, that's not my concern. My concern is that _when_ there is a read/write error (which are completely normal events with today's hard drive technology), the drive just gives up right away instead of making a few attempts. This could easily translate into (silently!) lost data in a single-disk scenario.
- pkaye 7y agoI think this is called TLER (Time Limited Error Recovery.) https://en.wikipedia.org/wiki/Error_recovery_control https://en.wikipedia.org/wiki/Error_recovery_control
- kstrauser 7y agoThat's exactly correct: see https://en.wikipedia.org/wiki/Error_recovery_control https://en.wikipedia.org/wiki/Error_recovery_control for details. Basically, NAS drives have a hard limit on how long they'll try to recover from errors before just reported the failure back to the RAID controller so that it can handle them.
- flyinghamster 7y agoYou can set the TLER value via smartctl, though that might not work through a USB interface. smartctl -l scterc,<READTIME>,<WRITETIME> /dev/xxxx WD Red drives should retain this setting across reboots. Some drives don't, and some don't support the command.
- bluGill 7y agoIf you are ever where this happens the drive is end of life and should be tossed and the new one rebuilt from backups. You do have backups right... Drives fail without notice often