Areca ARC-1110 User Manual

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In an effort to help users avoid data loss, disk manufacturers are 

now incorporating logic into their drives that acts as an "early 

warning system" for pending drive problems. This system is called 

S.M.A.R.T. The disk integrated controller works with multiple 

sensors to monitor various aspects of the drive's performance, 

determines from this information if the drive is behaving normally 

or not, and makes available status information to RAID controller 

firmware that probes the drive and look at it.

The SMART can often predict a problem before failure occurs. 

The controllers will recognize a SMART error code and notify the 

administer of an impending hard drive failure.

Under normal operation, even initially defect-free drive media can 

develop defects. This is a common phenomenon. The bit density 

and rotational speed of disks is increasing every year, and so is 

the potential of problems. Usually a drive can internally remap 

bad sectors without external help using cyclic redundancy check 

(CRC) checksums stored at the end of each sector.  

SATA drives perform automatic defect re-assignment for both 

read and write errors. Writes are always completed - if a location 

to be written is found to be defective, the drive will automatically 

relocate that write command to a new location and map out the 

defective location. If there is a recoverable read error, the cor-

rect data will be transferred to the host and that location will be 

tested by the drive to be certain the location is not defective. If 

it is found to have a defect, data will be automatically relocated, 

and the defective location is mapped out to prevent future write 

attempts. 

In the event of an unrecoverable read error, the error will be 

reported to the host and the location flagged as potentially defec-

tive. A subsequent write to that location will initiate a sector test 

and relocation should that location have a defect. Auto Reassign 

Sector does not affect disk subsystem performance because it