RAID arrays have built in features that can help reduce the likelihood of a failed hard drive, data loss, and a data recovery emergency.
The hard drives from popular manufacturers, including Western Digital and Samsung/Hitachi, all have different features that permit the system administrator, or whoever has configured the RAID array to configure how long a drive's firmware can spend recovering from a read or write error.
Western Digital calls this Error Recovery Control (ERC), while Samsung/Hitachi calls it Time-Limited Error Recovery (TLER). The generic name for this feature in other hard drives is Command Completion Time Limit (CCTL).
The idea is to limit the on-drive recovery time, leaving recovery to the RAID controller to prevent the possibility of performance degradation, which can lead to hard drive failure and, ultimately, RAID failure and the loss of mission critical data.
What Are the Best TLER or CCTL Settings?
Western Digital drives ship with TLER enabled at zero seconds, which means the hard drive itself will perform error recovery only in microseconds, well before the RAID controller's time out threshold. If TLER is not enabled and the drive times out, the RAID array will have to be re-built and re-synchronized. Enabling TLER, or, in other cases, CCTL or ERC, creates a more stable RAID array.
TLER and CCTL in Stand-Alone Hard Disk Drives
If you are operating a hard disk drive independent of a RAID array, you'll want to disable TLER for greater reliability, permitting the hard disk's firmware to repair any errors as it is able. Hard disks are designed to correct for small read/write errors that may occur.
If read/write errors occur consistently and cannot be fixed by the drive's firmware, you could be facing a data recovery emergency. While you can still read files from the disk, create a back-up, and then change out your hard drive before it fails completely.
Missed Your Chance to Create a Back-up?
Often, we don't realize we are facing a potential hard disk failure until it is too late and our hard drive fails to boot. If this happens, don't worry. Power down your machine and call 24 Hour Data. Do not attempt do-it-yourself data recovery, which could cause irrevocable damage to your hard disk drive. 24 Hour Data has decades of experience in Western Digital, Toshiba, Samsung/Hitachi, Seagate and other popular brands of hard disk drive and RAID drive recovery.