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Operating OnLine 3-53
Change Pathname of Archive Tape Device
If you change the pathname to /dev/null, the change proceeds more
smoothly if you make the change while OnLine is offline. If TAPEDEV is set
to /dev/null, you cannot perform a restore.
The tape device specified by the pathname must perform a rewind before
opening and on closing.
If you are logged in as user informix, you can change the value of
TAPEDEV
from within DB-Monitor or from the command line. If you are logged in as
root, you must use the command-line option.
Preliminary Considerations
Tape devices must rewind before opening and on closing to be compatible
with OnLine operation. The reason for this is a series of checks that OnLine
performs before writing to a tape.
Whenever OnLine attempts to write to any tape other than the first tape in a
multivolume backup or archive, OnLine first reads the tape header to ensure
the tape is available for use. Then the device is closed and reopened. OnLine
assumes the tape was rewound on closing and begins to write.
Whenever OnLine attempts to read a tape, it first reads the header and looks
for the correct information. OnLine cannot find the correct header infor-
mation at the start of the tape if the tape device did not rewind on closing
during the write process.
Create a level-0 archive immediately after you change the value of TAPEDEV
to ensure a proper restore. This is done for two reasons.
First, the OnLine restore procedure cannot switch tape devices as it attempts
to read the archive tapes. If the physical characteristics of the archive tapes
change during the restore, either because of a new block size or tape size, the
restore fails.
Second, the restore fails if the tape device specified as TAPEDEV at the time of
the level-0 archive is unavailable when the restore begins.
Important: At the beginning of a restore, the OnLine configuration, including
archive devices, must reflect the configuration as it was when the level-0 archive was
created.