Introduction to Data Management

Managing Data on the Tandem Systems
15873 Tandem Computers Incorporated 2-5
For example, you can use the Network Statistics System (NSS) to detect major
problems and impediments. NSS monitors and collects performance statistics on all
nodes, CPUs, and EXPAND line handlers. Then, you can use the MEASURE system
performance measurement tool for more detailed analysis. MEASURE continuously
collects statistics on disk drives, files, processes, transactions, and terminals as well as
CPUs and line handlers. Finally, you can pass the data generated by MEASURE to the
SURVEYOR performance management tool, which refines, reduces, and formats the
data and stores it in a performance database. Through SURVEYOR, you can use this
database for system and network analysis and tuning, evaluating current performance
and adjusting components for best overall system efficiency. Also, through
SURVEYOR, you can do capacity planning, analyzing trends in performance and
resource usage to forecast the resources you will need to support increased system
workloads. With still another tool, the ENCORE stress test generator, you can
determine how particular applications will perform under varying workloads.
Database Integrity for
Reliable Online
Operation
Even if a system offers the most advanced processing capabilities, it is equally
important that the data it maintains is always available and trustworthy. In an active
processing system, even a single corrupted data element can contaminate an entire
database. When this occurs, it can take weeks to find the cause of the error and
additional days to restore the database to an accurate state. Therefore, a really
workable system must protect against corruption or loss of data caused by system or
disk-drive failure.
Tandem systems offer this protection through several software products. The
GUARDIAN 90 operating system protects your data by running all I/O processes as
continuous process pairs. If a CPU, I/O channel, or I/O controller fails during any
update to the database, the NonStop transaction processing software either
successfully completes the update or fully backs it out. Furthermore, the operating
system checks to ensure that records are not duplicated during a failure.
The GUARDIAN operating system offers several other features that support database
integrity: structural integrity for files, storage-media protection, and data-sharing
protection. Also, the data management software includes a powerful application aid
that provides integrity from the standpoint of data consistency—the Transaction
Monitoring Facility (TMF), discussed later in this section.
At the network level, if a data path fails, the EXPAND data communication software
selects the best alternate path, ensuring data integrity at every node in the network.
Furthermore, EXPAND uses an end-to-end protocol to ensure that a message arrives
at its planned destination even if an intervening node or other hardware resource
involved in the transmission fails.
Finally, mirrored disks and the Remote Duplicate Database Facility (RDF) provide
additional backup by enabling you to generate and maintain a duplicate copy of
critical databases dynamically.