TMF Reference Manual (G06.24+)

TMFCOM Tape Media Considerations
HP NonStop TMF Reference Manual—522418-002
4-4
Using the VERIFYTAPE Option
Using the VERIFYTAPE Option
In the ALTER AUDITDUMP and DUMP FILES commands, the VERIFYTAPE option
determines whether a tape is verified after a dump is written to the tape. When the
VERIFYTAPE option is in effect, TMF examines the tape volume for data integrity after
the tape is written. This examination involves reading the volume labels, file labels,
data records, and checksums.
The improved data accuracy for the newer tape drives and controllers decreases
potential risk and the need for verification. In any event, some verification always
takes place at the tape-drive process level, regardless of whether VERIFYTAPE is set
to ON or OFF. If you feel that you need the extra verification provided by the
VERIFYTAPE option, use VERIFYTAPE on a trial basis and assess the impact on
system performance. If performance falls below an acceptable level for your purposes,
protect your data by using the COPIES 2 option instead of VERIFYTAPE. The
COPIES 2 option provides you with an extra copy of the dump tape.
Using the COPIES Option
In the ALTER AUDITDUMP and DUMP FILES commands, the COPIES option
determines the number of copies made of each dump directed to tape. These copies
can be produced in series or in parallel. In many cases, you will find that COPIES 1,
which produces one copy and which is the default, is sufficient. Although producing
multiple copies is sometimes recommended as insurance against a media failure
during the dump, this action does involve additional processing time and overhead.
Furthermore, the improved technology of the newer tape drives and controllers
decreases the potential risk of having just one copy. However, consider all relevant
factors at your site. If you decide you need multiple copies, and you are using the
newer controllers and drives, the high speed of these units can produce these copies
more efficiently if you specify COPIES 2 PARALLEL.
Choosing the Proper BLOCKSIZE
In the ALTER AUDITDUMP and DUMP FILES commands, the BLOCKSIZE option sets
the block length at which data is written to tape. For greatest efficiency, in most cases,
HP recommends you set the BLOCKSIZE to 52 (for 52K bytes). However, if your tape
drive is on a remote node connected through an EXPAND communication network, you
should set the BLOCKSIZE based on the bandwidth available.
Selecting a Tape Drive Model Type
If you have a choice of tape-drive model types, select a new device (such as a
cartridge tape drive, DAT device, or DLT device) rather than an open-reel tape drive.
The newer tape drives and devices are more reliable, and their tapes hold more data
and are easier to transport.
Along with your tape drive, use autoloaders or cartridge magazines for rapid tape
loading and automated cartridge systems to handle very large volumes of tapes.