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== Standalone vs. RAID considerations ==
It is best for TLER to be "enabled" when in a RAID array to prevent the recovery time from a disk read or write error from exceeding the RAID implementation's timeout threshold. If a drive times out, the hard disk will need to be manually re-added to the array, requiring a re-build and re-synchronization of the hard disk. Enabling TLER seeks to prevent this by interrupting error correction before timeout, to report failures only for data segments. The result is increased reliability in a RAID array.
In a stand-alone configuration TLER should be disabled. As the drive is not redundant, reporting segments as failed will only increase manual intervention. Without a hardware RAID controller or a software RAID implementation to drop the disk, normal (no TLER) recovery ability is most stable.
In a software RAID configuration whether or not TLER is helpful is dependent on the operating system. For example in FreeBSD the ATA/CAM stack controls the timeouts, and is set to progressively increase the timeouts as they occur. Thus, if a desktop disk without TLER starts delaying a response to a sector read, FreeBSD will retry the read with successively longer timeouts to prevent prematurely dropping the disk out of the array.
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* [http://wdc.custhelp.com/app/answers/detail/a_id/1397/p/227,283/session/L3RpbWUvMTMyMTQzOTc4NS9zaWQvdVhvYmpmSms%3D Western Digital FAQ answer ID 1397: Difference between Desktop edition and RAID (Enterprise) edition drives]
* [http://www.wdc.com/wdproducts/library/other/2579-001098.pdf Time-Limited Error Recovery (TLER) Information Sheet], Western Digital, January 2013
* [https://web.archive.org/20071103042201/http://www.samsung.com:80/global/business/hdd/learningresource/whitepapers/LearningResource_CCTL.html Samsung CCTL]
[[Category:Rotating disc computer storage media]]
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