Reference Topics
447
B
Fragmenting tape backups can also speed up restores because NetBackup can
skip to the specific fragment before starting its search for a file. Otherwise, it
has to start at the very beginning of the backup and read tar headers until it
finds the desired file.
For the multiplexed format, see “Multiplexing Format” on page 447.
Note:
If an error occurs in a backup, the entire backup is discarded and the
backup restarts from the beginning, not from the fragment where the error
occurred.
Spanning Tapes
By default, NetBackup spans a backup image to another tape if it encounters
the end of media during a backup. The format is the same as explained above
for fragmented backups and the first fragment on the next tape begins with the
buffer of data where the end of media occurred:
First tape: MH * ... *BHn Image (frag 1) * *
Next tape: MH * BHn Image (frag2)* ... * EH *
On the first tape, NetBackup does not write an EH, and terminates the tape
with two tape marks.
Multiplexing Format
The tape format for multiplexed backups is:
MH * BH1 ... BHn Data...
Where:
• MH is the Media Header (1024 bytes).
• * is a Tape Mark.
• BH1 ... BHn are backup Headers (1024 bytes). One for each job that is part
of the set of jobs being multiplexed.
• Data is the data from the backup. By default, the data is in 64 kilobyte
blocks. Each block also contains 512 bytes that are reserved for multiplexing
control information (less than 1% of the total data) and to identify the
backup that the block corresponds to.
NetBackup 3.2 System Administrator's Guide for Windows NT
NetBackup 3.2 System Administrator's Guide for Windows NT
