Exabyte EXB-8505 8mm manual Error Detection, Correction, and Recovery Procedures

3Functional Description

Error Detection, Correction, and Recovery Procedures

As the tape drive writes data to tape, it integrates error correction code (ECC) and physical-block cyclic redundancy check (CRC) bytes with each physical block. After it writes data, the tape drive uses the ECC and CRC to perform a read-after-write check to ensure data reliability. By using read-after-write error checking and sophisticated error correction procedures, the tape drive offers a non-recoverable error rate of less than one bit in 1017 bits read.

Error Correction Code (ECC)

The Reed/Solomon ECC algorithms can correct a burst as long as 264 consecutive bytes in error and as many as 80 additional random errors in each physical data block. The ECC is capable of multiple burst and random error corrections. It has been designed to be extremely effective against the types of error patterns that may occur in cartridge tape subsystems that use helical-scan technology.

Cyclic Redundancy Check (CRC)

The tape drive also adds two bytes of CRC data to every physical block on tape. The CRC data is used in the read-after-write check.

Read-After-Write Checking

The tape drive performs a read-after-write check of the recorded user data to ensure full data reliability. If the tape drive determines that any data blocks should be rewritten, it rewrites the data without requiring host intervention or repositioning of the tape.

For more information about how the tape drive corrects data during the read-after-write check, refer to Chapter 6.

3-6	EXB-8205 and EXB-8505	510504
	(Standard and XL)