RDF/IMP and IMPX System Management Manual (RDF 1.3+)

Preparing the RDF Environment
Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001
2-3
Data Communication (Expand) Resources
RDF is designed to extract audit information from the primary system and transmit it to
the backup system as quickly as possible, limiting the number of transactions that could
be lost if a disaster should occur at the site of the primary system. If RDF has to wait for
the Expand subsystem, RDF might not be able to stay current with transactions
occurring on the primary system.
To estimate the data communications resources needed for RDF, calculate the amount of
audit trail data generated per second during peak loads. If your business has seasonal
peaks, such as holidays or the ends of calendar quarters, consider the peak rate at those
times.
Use the following sampling process once an hour for two weeks to establish your needs:
1. Enter a FUP INFO command for the current TMF MAT and record the end-of-file
(EOF) value; for example:
FUP INFO $AUDIT.ZTMFAT.*
2. Enter a FUP INFO command for the current MAT 5 minutes later and record the
EOF value; for example:
FUP INFO $AUDIT.ZTMFAT.*
3. If all the TMF audit data is generated on volumes protected by RDF, subtract the
first EOF value from the second EOF value to obtain the number of bytes generated
during the 5-minute period. Then divide the number of bytes by 300 seconds to
determine the amount of audit data generated in a second; for example:
(11653120-11292672)/300 = 1202 bytes per second
The extractor does not necessarily transmit all audit records associated with a particular
transaction. For example, audit information associated with physical operations is not
transmitted. The reason for this is that the backup database is maintained as a logically
identical copy of the primary database, not as a physically identical copy.
The data communications link should have at least two paths (multi-line Expand). Each
path should go through different communications carrier paths or switches, and each
should be able to transmit the peak data rate.
It is almost impossible to calculate the RDF audit transmission rate from the TMF audit
generation rate alone.
Compaq has developed a sizing tool that can be used to predict accurately the Expand
bandwidth requirements between the primary and backup systems by simulating the
RDF extractor. That utility reads the TMF master audit trail and generates detailed
information about TMF audit generation and RDF audit transmission activity. This
information is particularly useful when a single system supports multiple applications
CODE EOF LAST MODIF OWNER RWEP TYPE REC BLOCK
$AUDIT.ZTMFAT
AA000003 134 11292672 10:05 -1 GGGG
CODE EOF LAST MODIF OWNER RWEP TYPE REC BLOCK
$AUDIT.ZTMFAT
AA000003 134 11653120 10:10 -1 GGGG