HP-UX Reference (11i v1 05/09) - 1M System Administration Commands A-M (vol 3)

f
fbackup(1M) fbackup(1M)
• When using magnetic tape devices, the main blocks of information (tape label, volume header,
index, data) are separated by EOF marks. fbackup
also checkpoints the media periodically to
enhance error recovery. If a write error is detected, the user normally has two options: (1) a new
volume can be mounted and that volume rewritten from the beginning; or, (2) if the volume is not
too severely damaged, the good data before the error can be saved, and the write error is treated
as a normal end-of-media condition. The blocks of data with their checkpoint records are also
separated by EOF marks. In addition, for DDS tape drives, if fast search marks are supported,
these will be used to enhance selective recovery speed by placing them between blocks of files.
Similarly on DLT tape drives, faster selective recovery is achieved using the EOF marks used for
checkpointing in conjunction with the file sizes given in the index.
• For a magneto-optical device, a disk, a file, or standard output, there are no special marks separat-
ing the information pieces; the backup is always a single file (volume).
fbackup provides the ability to use UCB-mode tape drives. This makes it possible to overlap the tape
rewind times if two or more tape drives are connected to the system.
Set-up
There are several things the user will want to consider when setting up fbackup for regular use. These
include type of device and media, full versus incremental frequency, amount of logging information to keep
on-line, structure of the graph file, and on-line versus off-line backup.
The type of device used for backups can affect such things as media expenses, ability to do unattended
backups, and speed of the backup. Using 36-track tapes will probably result in the highest performance,
but require user intervention for changing tapes. Both DLT and DDS autochangers and libraries can pro-
vide unattended backups. A magneto-optical autochanger can also provide an unattended backup for a
large system and long life media, however the media cost is high. Lower cost and good performance can be
achieved with a single DLT tape drive, but multi-volume backups must be attended.
It is also important to consider how often full backups should be made, and how many incremental backups
to make between full backups. Time periods can be used, such as a full backup every Friday and incremen-
tals on all other days. Media capacities can be used if incremental backups need to run unattended. The
availability of personnel to change media can also be an important factor as well as the length of time
needed for the backup. Other factors may affect the need for full and incremental backup combinations
such as contractual or legal requirements.
If backup information (output from the
-V or -I options) is kept on-line, the required storage space must
also be considered. Index file sizes are hard to predict in advance because they depend on system
configuration. Each volume header file takes less than 1536 bytes. Of course the more information that is
kept on-line, the faster locating a backup media for a recovery will be.
There are several ways to structure the graph file or files used in a system backup. The first decision
involves whether to use one or more than one graph file for the backup. Using one file is simpler, but less
flexible. Using two or more graph files simplifies splitting backups into logical sets. For example, one
graph file can be used for system disks where changes tend to be less frequent, and another graph file for
the users area. Thus two different policies can be implemented for full and incremental backups.
fbackup was designed to allow backups while the system is in use by providing the capability to retry an
active file. When absolute consistency on a full backup is important, the system should probably be in
single-user mode. However, incremental backups can be made while the system is in normal use, thus
improving system up-time.
Options
-c config config is the name of the configuration file, and can contain values for the following parame-
ters:
• Number of 1024-byte blocks per record.
• Number of records of shared memory to allocate.
• Number of records between checkpoints. Since the EOF marks between checkpoints
are also used for fast searching on DLT tape drives, changing the checkpoint fre-
quency may also affect selective recovery speed (see WARNINGS section).
• Number of file-reader processes.
• Maximum number of times fbackup is to retry an active file.
• Maximum number of bytes of media to use while retrying the backup of an active
file.
HP-UX 11i Version 1: September 2005 − 2 − Hewlett-Packard Company Section 1M−−215