TLER in end-user systems

In your home PC, you're better off without TLER.

TLER (Time Limited Error Recovery) is a feature of WD hard drives. It limits the time the hard drive spends attempting to recover from a read error. Most other manufacturers has similar options, under different names.

TLER is designed to improve performance, not reliability. TLER kicks in when the hard drive experiences an uncorrectable read error (most likely due to a bad sector). The drive with a bad sector should generally be replaced as soon as possible, because it is likely to produce another bad sector soon. Pre-TLER result would be the RAID controller dropping the drive offline. With TLER, the missing data is recovered from RAID redundancy and the drive remains online.

With a typical consumer-grade maintenance this effectively hides the problem until the drive fails completely, thereby increasing the vulnerability window of a fault tolerant arrays. In an enterprise-grade systems, where continuous availability is important, this is good. A consumer-grade system, where shutdown is not a problem, is better be shut down immediately once a read error occurs.


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