The many variations on the options available from the command line can be daunting for a first time user. For most operations, only a small number of options are used.
If you have ever used the UNIX command ‘tar’, you’re already a good way towards understanding the way BRU operates from the command line. To simplify things, let’s examine some of the basic properties of any BRU backup:
Once you know these items, you need to examine the various modes and options that BRU provides. These include:
-c – Create (backup) a BRU backup volume
-x – Extract (restore) files from a BRU backup volume
-t – Table of Contents (file list) of a BRU backup volume
-i – Inspect (verify) the contents of a BRU backup volume
-e – Estimate the number of volumes a BRU backup will require
-d – Difference (compare) the contents of a BRU backup volume with the original files on the file system
-v – Verbosity level (up to five v’s may be specified)
-f – What backup device should be accessed
BRU’s command line looks like this:
bru -mode -[options] [-f device] [path]
With these basic modes and options, all basic backup and restore functions can be performed. For example, to backup the contents of the entire system to the first SCSI tape drive under Linux, we would issue the following BRU command:
bru -cvf tape0 /
This will backup the entire system to the tape drive /dev/st0. To examine the contents of a tape made in this manner, we could issue the command:
bru -tvf tape0
Notice that we don’t have to specify a file path for a listing of the tape.
To restore the entire backup to its original path, we would use:
bru -xvf tape0
This call would automatically restore all files to their original locations.
To verify the contents of a BRU backup volume, there are two options available. The first is OWC’ recommended option as it requires only the tape drive and BRU to operate. This is the inspect (-i) mode.
bru -ivf tape0
This verification rereads each buffer block written on the backup volume and recalculates the block’s checksum. BRU then compares this calculated checksum with the checksum that was written in the buffer block header. If an incorrect value is detected, BRU will issue a warning that the checksum is bad for the particular file that the error occurred within. However, BRU will restore the available data in the file and any additional data on the backup – unlike other applications which abort at the first sign of a tape error.
The second option is a more widely used method that requires both the backup volume and the original data. This mechanism is called the difference (-d) mode.
bru -dvf tape0
This option reads the data from the tape and performs a bit-by-bit comparison with the original data from the file system. Of course, this mechanism will report problems if files have changed on the file system since the backup was made. This is what makes the inspect mode verification the preferred option for verifying tapes.