How the dump command writes and stores data on tape

About this section

The dump command transfers a number of blocks of data at a time to an output file on tape. This section provides information about how the command writes and stores these blocks of data, which helps you decide the dump command format appropriate for your backup.

Meaning of tape block

A tape block is 1 kilobyte of data. In the dump command, you can specify the number of tape blocks that are transferred in each write operation. This number is called the "blocking factor."

Caution: If you plan to restore the backed-up files on a computer other than the filer, make sure that the blocking factor you choose does not exceed the maximum blocking factor supported by that computer. If you use a filer to restore the backup data, the blocking factor must not exceed 63.

Meaning of tape file

A tape file is a dump output file on tape. It can also be an entire tape. You can back up a dump path to one tape file on a tape, multiple tape files on a tape, or multiple tape files on multiple tapes.

In the dump command, you can specify the maximum size of the tape file in terms of tape blocks. For example, if you want the maximum tape file to be 2 GB, specify 2,097,151. (That is, the largest tape file can contain 2,097,151 tape blocks, which are 1 kilobyte each.)

Caution: If the backed-up files are to be restored on a computer other than the filer, make sure that the tape file size you choose does not exceed the maximum tape file size supported by that computer. If you use a filer to restore the backup data, the tape file size can be as large as a single tape.

When the dump command writes to multiple tape files

When the data being backed up exceeds the capacity of a tape, the dump command automatically writes to the next tape file specified in the command. If the current tape file is the last tape file listed on the dump command, the filer prompts you to load another tape.

If you specify the maximum tape file size in the dump command, the command writes to the next tape file when the backup data reaches that size, regardless of the amount of space left in the current tape.

A tape can contain multiple tape files, but any tape must contain at least one complete tape file.

Different types of tape files

The dump command can use these types of tape files:

Local or remote. (Refer to "Devices used by the dump command" for more information about where the tape devices can be located.)
Rewind or norewind. If the tape file is a rewind file, the filer rewinds the tape after it finishes writing the tape file. If you want the dump command to write multiple tape files on the same tape, specify norewind tape files in the dump command.
The name of a norewind tape file begins with an n (for example, nrst0a); the name of a rewind tape file begins with an r (for example, rst0a).
Unload/reload tape files. These tape files apply only if you are backing up to tapes in tape stackers. When you use these tape files, the dump command unloads the tape when it reaches the end of tape, and then the tape stacker reloads another tape.
The name of an unload/reload tape file begins with a u (for example, urst0a).

An unload/reload tape file cannot be a norewind tape file. For example, do not specify unrst0a.

Note: If the tape stacker is attached to a remote host, the dump command can reload the tape only if that host supports automatic reloading.
Standard output, which is specified as - in the dump command.

Part No. 210-02334
File: dump3.htm
Last updated: 02/24/99 12:17:01