NonStop Systems Introduction

Requirements of ZLE Systems
NonStop Systems Introduction—527825-001
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Data Security
check the customer’s credit card transaction history, including purchases, refunds, and
exchanges. The ZLE software would return a recommendation based on its
examination of the customer’s history. But the recommendation is only as reliable as
the data; any missing or incorrect information in the transaction history could result in
an unreliable recommendation.
If a processor, disk drive, or disk drive controller fails, the dangers to data integrity are
even greater. Many applications, each with multiple concurrent users, could be
executing at the point of failure. These applications could be in the process of
updating hundreds of records on the data store at the moment of failure. If we have no
way of knowing which updates were successful and which ones did not get recorded in
the data store, the data store is no longer useful because it no longer reflects the real
state of things.
A ZLE system must ensure that transaction data and data in the data store are correct
and consistent at all times. The need for data integrity imposes the following three
requirements:
•
The system must preserve data as received from the end user or other source,
even if a system component fails while the system is processing the data.
•
The system must back out those transactions that cannot transform the data store
from one consistent state to another.
•
The system must restore the data store to its correct and operational state in the
event of a failure such as a head crash on a disk drive or the loss of a pair of disk
drives.
Data Security
ZLE applications make data resources available to multiple end users of business
applications. Such ZLE applications must be able to restrict the use of data resources
to a subset of the total user population, or the business loses control of its resources.
For example, the data store might contain credit card information for an order-entry
application running on an operational system. The server that runs the application that
accesses the data store must provide a security mechanism that prevents
unauthorized users from viewing or altering records.
In addition, the system must offer a security mechanism that restricts authorized users
to subsets of data. For example, each manager who has access to the database must
be able to view and alter only those records that pertain to that manager’s employees.
High Performance
If a ZLE system is to provide anything close to zero latency, the ZLE applications and
data store must be able to handle massive workloads without overwhelming the
processing capabilities of the ZLE system. Furthermore, as the business grows, the
system must be able to handle the increasing volume of transactions with no loss of