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subject: How to backup Linux system using Dump [print this page]

How to backup Linux system using Dump
How to backup Linux system using Dump

The dump tool works by making a copy of an entire file system. The restore tool can then take this copy and pull any and all files from it.

To support incremental backups, dump uses the concept of dump levels. A dump level of 0 means afull backup. Any dump level above0 is an incremental relative to the last time a dump with a lower dump level occurred. For example, a dump level of 1 covers all the changes to the file system since the last level 0 dump, a dump level of 2 covers all of the changes to the file system since the last level 1 dump, and so onall the way through dump level 9. Consider a case in which you have three dumps: the first is a level 0, the second is a level 1, and the third is also a level 1. The first dump is, of course, afull backup. The second dump (level 1) contains all the changes made since the first dump. The third dump (also a level 1) also has all the changes.

The dump utility stores all the information about its dumps in the /etc/dumpdates file.

This file lists each backed-up file system, when it was backed up, and at what dump level.

Given this information, you can determine which tape to use for a restore. For example, if you

perform level 0 dumps on Monday, level 1 incrementals on Tuesday and Wednesday, and then

level 2 incrementals on Thursday and Friday, a file that was last modified on Tuesday but got

accidentally erased on Friday can be restored from Tuesday night's incremental backup.

A file that was last modified during the preceding week will be on Monday's level 0 tape.

Using dump

The dump tool is a command-line utility. It takes many parameters,

For example,here is thecommand to perform a level 0 dump to /dev/st0 of the /dev/hda1

file system:

[root@scribe /root]# dump -0 -f /dev/st0 /dev/hda1

dump Parameter Description

n Specifies the dump level, where n is a number between 0 and 9. For

example, 0 would perform afull backup.

b blocksize Sets the dump block size to blocksize, which is measured in kilobytes. If you

are backing up many large files, using a larger block size will increase

performance. You may need to carefully adjust this to match the capabilities

of your tape system.

B count Specifies a number ( count) of records per tape to be dumped. If there is

more data to dump than there is tape space, dump will prompt you to insert

a new tape.

f filename Specifies a location ( filename) for the resulting dump file. You can make the

dump file a normal file that resides on another file system, or you can write

the dump file to the tape device. The SCSI tape device is /dev/st0.

u Updates the /etc/dumpdates file after a successful dump.

d density Specifies the density of the tape in bits per inch.

s size Specifies the size of the tape in feet.

a Bypasses all tape-length calculations and writes until an end-of-media signal

is returned. This works best for most modern tape drives and is particularly

useful for appending data to existing tapes. This is the default mode.

z or j Compresses each data block. The z parameter uses zlib compression, while

j uses bzlib. Either option can be immediately followed with a number, if

you want to specify the compression level, or white space, if you want to

accept the default compression level of 2. Your tape drive must be able to

support variable-length blocks to be able to use this feature. If your tape

system has hardware compression built in, don't use both the hardware

compression and this option together, or your files will likely increase in size.

Using dump to Back Up an Entire System

The dump utility works by making an

archive of one file system. If your entire system comprises multiple file systems, you need to

run dump for every file system. Since dump creates its output as a single, large file, you can

store multiple dumps to a single tape by using a nonrewinding tape device.

Assuming we're backing up to a SCSI tape device, /dev/nst0, we must first decide which

file systems we're backing up. This information is in the /etc/fstab file. Obviously, we don't

want tobackup filessuch as /dev/cdrom, so we skip those. Depending on our data, we may or

may not want to back up certainpartitions(such as swap and /tmp).

Let's assume this leaves us with /dev/hda1, /dev/hda3, /dev/hda5, and /dev/hda6. To

back uptheseto /dev/nst0, compressing them along the way, we would issue the following

series of commands:

[root@scribe /root]# mt -f /dev/nst0 rewind

[root@scribe /root]# dump -0uz -f /dev/nst0 /dev/hda1

[root@scribe /root]# dump -0uz -f /dev/nst0 /dev/hda3

[root@scribe /root]# dump -0uz -f /dev/nst0 /dev/hda5

[root@scribe /root]# dump -0uz -f /dev/nst0 /dev/hda6

[root@scribe /root]# mt -f /dev/nst0 rewind

[root@scribe /root]# mt -f /dev/nst0 eject

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