Product manual

CDA 7 5630 Product Manual
5-12 77 A1 69UP Rev00
5.3 Data Integrity Protection
CDA 7 preserves data integrity by performing extensive error checking and
correction on all data and addresses it passes internally.
5.3.1 Error Checking, Correction, and Data Integrity Protection
In conventional disk, the subsystem adds error checking and correction bytes to
each data record field, as shown in the following figure. It uses these error
checking and correction bytes to check the data and correct it if possible. If it
detects an uncorrectable error, the disk subsystem informs the host that it has
encountered bad data to avoid affecting data integrity.
DATA RECORD
ECC
BYTES
Figure 5-2. Data Record Format for Conventional Disk
CDA 7, like conventional disk, performs this level of error checking and correction
when it passes data and addresses. CDA 7, however, goes further to ensure that the
information passed belongs to the record specified. It does this by including
additional bytes with the data field of each record. These bytes contain the record
ID and a double LRC (Longitude Redundancy Code) check byte as shown in the
following figure. CDA 7 uses these bytes to check that the data is from the
specified record and alarms the host if it is not. This second level of protection
further ensures data integrity by preventing incorrect data from being transferred.
DATA RECORD
EMBEDDED
ID
ECC
BYTES
LRC
BYTES
Figure 5-3. CDA 7 Data Record Format
CDA 7 has three levels of error detection. Should an error be undetected at one
level, it will be detected at one of the other levels.
CDA 7 uses the following error correction and detection methods:
• Parity
• Error Checking and Correction (ECC)
• Longitude Redundancy Code (LRC)