HP StorageWorks P9000 User Manual page 8

Detection of corrupt data: If the Database Validator function detects corrupt data, the I/O operation
from the host is rejected, just as if there had been a hardware failure. The error code indicates
"H.A.R.D. failure". If the data corruption problem is transient, the condition may clear when the
host retries the I/O. If there is no successful retry operation, the application I/O operation fails,
and the Oracle update transaction does not complete. The solution resource manager logs the
H.A.R.D. error to the host's syslog.
Hardware acceleration: The P9500 CHAs include hardware acceleration of Database Validator
checksum computation. The HP implementation of checksum validation using hardware acceleration
minimizes performance impact (the impact depends on the system environment).
Multiple levels of checking: In addition to the verification of checksums for overall database blocks,
the P9500 also performs checksum validation for lower-level data structures specific to the type of
file. Tablespace and control files have one type of lower-level checking, while redo log files have
another type. HP's additional lower-level data structure checking further increases protection. When
Database Validator is turned on using RAID Manager, the type of data (data file vs. redo log) must
be specified so that the correct type of lower-level data structure validation is performed.
Read operations: No additional Oracle checksum validation is done for read operations. The
Oracle application verifies the checksum at the application end. (The P9500 always performs its
own internal checksum verification on reads, and hence always resends the same data originally
received.)
Database Validator validates the check data at every write operation to the storage and checks
out the abnormal data immediately after a failure occurs. Database Validator blocks the incorrect
write request from the host, returns a SCSI Check Condition error, and protects the correct data in
the storage. The Oracle database would stop itself as an error or separate the damaged table,
depending on the error situation, but the administrator can recover the database without the loss
of data consistency because any invalid data is not written to the storage, nor is any valid data
overwritten.
8 About Database Validator operations