AMCC 720-0138-00 manual What Verification Does, Verification of Non-Redundant Units

Background Tasks

What Verification Does

For a RAID 1 or RAID 10 unit, a verify compares the data of one mirror with the other. For RAID 5, a verify calculates RAID 5 parity and compares it to what is written on the disk drive.

Verification checks each sector on a drive. This is important, because day-to- day use of the media may leave many sectors on a drive unused or unchecked for long periods of time. This can result in errors occurring during user operation. Periodic verification of the media allows the disk drive firmware to take corrective actions on problem areas on the disk, minimizing the occurrence of uncorrectable read and write errors.

Verifies can be scheduled to run at preferred times or can be run automatically during the Verify schedule window, if scheduling and the Auto Verify feature are enabled.

Verification of Non-Redundant Units

Verification of non-redundant units (single disks, spares, and RAID 0 units) read each sector of a drive, sequentially. If a sector can’t be read, it is flagged as unreadable, and the next time the controller writes to that location, the drive reallocates the data to a different sector.

Verification of Redundant Units

Verification of redundant units also reads each sector, working from lowest block to highest block. If verification cannot read data in a sector, dynamic sector repair is used to recover the lost data from the redundant drive or drives; this recovered data is written to the problem sector. This forces the drive to reallocate the defective sector with a good spare sector.

If the verify unit process determines that the mirrored drives are not identical or the parity is not correct, the error is corrected. For RAID 1 and 10, this involves copying the miscompared data from the lower port(s) to the higher port(s) of the mirror. For RAID 5 this involves recalculating and rewriting the RAID 5 parity that was incorrect. AEN 36 (“Verify detected and fixed data/ parity mismatch”) is posted to the Alarms page.

For RAID 1 and 10, initialization involves copying the data from the lower port(s) to the higher port(s) of the mirror. For RAID 5 this involves recalculating and rewriting the RAID 5 parity for the entire unit. If the unit is not redundant, a file-system check is recommended to correct the issue. If the errors persist and cannot be overwritten from a backup copy, perform a final incremental backup. You will need to replace the defective drive, recreate the unit, and reinstall the data.

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