Grown Sector Media Error Protection

Grown Sector Media Error Protection

As the drive attempts to read data in a read request, it determines that Record 1 of Disk 1 has a bad sector, as pictured below. If the media error is minor, the drive corrects or remaps the information using the drive ECC information, which is transparent to the RAID array.

If the disk cannot recreate the information from the ECC information on the drive, the adapter determines if the data is still lost, as it was without RAID support. In such a case, ServeRAID adapters can recognize the fault and re-create the data from redundant information stored on other drives.

For example:

1.  Record 1 in the diagram is corrected from data  stored in Record 2 on Drive 2 and check sum information on Drive 3.

    The ServeRAID adapter requests that Record 1 be rewritten.

2.  The drive remaps the bad sector elsewhere on  the drive. Record 1 now has good data.

In this example, RAID-5 has increased the availability of the information by re-creating data that otherwise would have been lost. It is initially assumed that this process was initiated by accessing this data on the drive. Were this data not accessed, this error would not be detected. This problem can be significant if a catastrophic failure occurs before the data is corrected.