System Backup Strategies Objective At the conclusion of this module, the student will be able to: describe the necessity for creating a backup regimen describe the advantages and disadvantages of the most commonly used backup devices describe the basic syntax and usage of the dump and restore commands use the dump command to archive a filesystem explain the limitations of the dump command and precautions for its use describe the advantages of different backup sequences restore an individual file from a filesystem archive restore an entire filesystem from an archive describe various archiving options available on UNIX systems Backup 2 1
Designing a Backup Strategy In designing a backup strategy, we should ask: 1. What happens if I loose my data? For a bank consider what happens if they lose an atm withdrawal? 2. How long can we afford to be down if we have to recover data from archive? 3. Could our organization function if we were down for a day or more while data is restored? If you must have guaranteed access to data you might consider using some form of RAID disk storage RAID storage, coupled with optical or tape backup can deliver almost continuous uptime Backup 3 Backup Responsibility It is necessary to develop a thorough, and easily maintained backup procedure The first step in designing a backup strategy is to create a written policy that specifies: who is responsible for ensuring that backups occur what file systems and files need regular archiving Anything that is mission critical for the organization should be backed up regularly when backups be performed Backups should be conducted during slow hours because most backup programs will not properly archive a file if it is in use The policy should specify a backup time and all users should know the schedule where the backup tapes and media should be stored This should be a secure, cool, and dry place Some critical backups should be stored off campus which systems need backing up Decide which systems require a regular backup and the frequency what type of media should be used for backing up how to backup Backup 4 2
What to Backup As a backup policy is developed make a decision on what needs to be backed up Differentiate between the operating system files and user files We need to archive the operating system (including /, /usr, /var, and /etc) only when significant changes occur We need to backup user files in /home much more frequently Since these directories may become very large, so we should schedule backups at off-peak times Usually Friday, Saturday, or Sunday nights for full backups Develop a strategy that backs up only those files that have changed since the last backup Backup 5 Backup Strategy Full aka level 0, archival, or epochal a complete archive of all files, including system and user files requires one set of media, but takes the longest time the mandatory part of all other strategies may be done on a weekly, monthly or quarterly basis frequency depends on how often system files are updated. Differential Backup of all files that were created or modified since the last full backup requires two sets of tapes The first tape contains the full backup The second contains a backup of all files created or changed since the full backup This option saves backup time, but requires more time to restore Backup 6 3
Backup Strategy Incremental This is more a complex method uses several sets of tapes to archive only those files with newer created or modified dates since the last backup A new tape is used for each backup Each new tape contains only files created or changed on the day of the backup When restoring, we must use the archival tape, then restore each tape for each day This option allows us to spend the least time backing up, but requires the most time when restoring Incremental backups pose the threat of operator error Network backup backing up filesystems from one machine onto a backup device connected to another machine referred to as a remote or network backup Backup 7 Disk Mirroring Disk Mirroring duplicates everything on one drive to another drive It is usually common for a system of this type to update the duplicate drive continuously with the most current information With RAID 1, the duplicate drive is written at the same time as the original This reduces or eliminates the recovery time in case of a disaster Many popular repositories of shareware and free software, like Tucows, uses disk mirroring It also reduces incoming traffic since users can visit a local mirror (in New Jersey, one of the Tucows mirrors is at Rutgers) to download software Backup 8 4
Comparison of Backup Media Backup 9 Types of Backup Devices and Media Tapes Tapes remain the most common archiving media Earlier, 9-mm tapes were the most common tape media, but 4- and 8-millimeter Digital Audio Tape (DAT) cartridges, about the size of an audiocassette, are now standard tape carts can hold from 20GB to 400GB CD-ROMs Re-writable CD-ROMs have become popular Highly secure or frequently hacked sites use read-only CD ROMS to store log files A CD jukebox contains multiple read-write drives and disks, which can then store up to five stacks of 100 CDs can back up multiple machines across a network DVD-ROMs Similar to CD s except each disk stores much more data some DVD Jukebox systems can hold up to 200 disks, and can write either CDs or DVDs Other Archiving Media SyQuest drives, Iomega ZIP, and JAZ drives can also be used Optical disks are similar to CDs, but they store from 100 MB to 1 GB per disk Firewire and USB or removable hard drives are also a possibility. Backup 10 5
dump and restore Dump ideal for archiving entire file systems originally developed for BSD, but is now been ported to all major versions of UNIX It is ideal for incremental backups because we can set it to use and modify the /etc/dumpdates file, which lists the date and level of the latest backup dump uses the syntax: dump option... argument... filesystem-to-backup restore allows us to retrieve the files we backed up using dump Using restore, we can retrieve a single file or entire filesystems Restore uses the syntax : restore options arguments file/directory Backup 11 Common dump Options Option/Meaning /Type s size of tape in feet Depends upon tape length. The 8-mm default is 2400. 5400 if combined with the c option. C use a tape cartridge Depends on the size of the tape often used with s d specifies tape density Recent versions of dump can autodetect tape lengths and density Depends on density. For 8-mm, 42500, or 1000 when used with the c option. 0-9 specifies the dump level The 0 option creates a full backup, while a 9 creates an incremental backup dump uses a zero-based count, which means that it begins counting at 0, not at 1 If we do not specify a level, dump defaults to 9 u Updates /etc/dumpdates Backup 12 6
Common dump Options Option/Meaning /Type f Name of device to write to supply a filename d specifies tape density Recent versions of dump can autodetect tape lengths and density Depends on density. For 8-mm, 42500, or 1000 when used with the c option. 0-9 specifies the dump level The 0 option creates a full backup, while a 9 creates an incremental backup dump uses a zero-based count, which means that it begins counting at 0, not at 1 If we do not specify a level, dump defaults to 9 u Updates /etc/dumpdates n Send a message when finished Backup 13 Common restore Options -I Launches restore in interactive mode -f Specifies the device to use If not specified, the default setting applies -r Restores the entire archive -x Restores only specified files -R Reads from a particular tape in a multivolume sequence -s Selects the specific backup tape (for use on jukeboxes) used with R option -t Lists the contents of the archive tape -v Verbose method Backup 14 7
Archiving the filesystem When we dump the filesystem, we must specify the dump level specify epochal, differential, or incremental backup the device where we wish to put the archive the file system to back up The table shows the special file name corresponding to a tape drive for various Linux/UNIX systems System File name AIX /dev/rfd0 IRIX /dev/tape HP-UX /dev/rmt/0 Linux /dev/tape Solaris /dev/rmt0 BSD../devices/pseudo/dump@0:dump Backup 15 Red Hat dump Example dump 0uf /dev/rft0 /dev/hda3 1 5 3 4 2 1. Specifies the entire filesystem (level 0) 2. on /dev/hda3 3. should be backed up to mag tape (f option combined with destination device) 4. at /dev/rft0 5. and that the dumpdate (u option) should be written to /etc/dumpdates Backup 16 8
Restoring a Filesystem To restore a lost or damaged file system, you must first create the partition and directory Assume we want to recreate the /home directory on hdb1 mkfs /dev/hdb1 mount /dev/hdb1/home cd /home restore rf /dev/rft0 The r option specifies that the entire archive on rft0 should be restored to the current directory Backup 17 Backups with cpio cpio was the original archiving utility It does not support backing up across a network, but is very useful when archiving entire file systems cpio Flags Options i extracts all files matching one or more of the given pattern arguments from the archive. o writes a new archive to the standard output, using the list of files read from the standard input b causes 16-bit words to be swapped within each long word and bytes to be swapped within each 16-bit word of each extracted file. d forces the creation of necessary intermediate directories if they do not already exist. v provides more verbose information than usual. cpio prints the names of files as it extracts them from or adds them to archives. Backup 18 9
Backups with tar tar is a versatile and popular tape archive command It may be used to produce archived backups on floppies or tapes, restores backups, and can be used by non-root users with read and write permissions The tar syntax is simpler that cpio, but it does not copy special files or empty directories Restoring individual files is much easier than with cpio you can start restoring from the volume that contains your wanted file We can define the name and characteristics of your default backup device in a file called /etc/default/tar This file can hold several such devices, which may be selected via the command line Backup 19 Backup Options with tar assign /dev/tape tar cvfk /dev/tape 1440 chap* The example here lists the c, v, f, k options c - creates a new archive file and starts writing at the beginning v verbose option causes tar to display filenames as they are archived f takes the /dev/tape argument as the target archive name Without this option, tar takes the default from a device name stored in /etc/default/tar also stores defaults such as blocking factor and volume size tar can also read and write from standard input and output which is useful for piping Backup 20 10
tar Option Syntax The first option letter must be either r, x, t, u, or c with no hyphens This first letter can be followed by one or more function modifiers with no intervening spaces or hyphens c vf (no hyphen before the c, vf are function modifiers Function modifiers need their arguments listed after the group of option letters in the correct sequence In the following example, the option letter c is followed by two modifiers f and k f takes the argument /dev/tape k takes the argument 1440 tar cvfk /dev/tape 1440 chap* Backup 21 AMANDA AMANDA - Advanced Maryland Automatic Network Disk Archiver - from the University of Maryland is a popular backup and restore solution The AMANDA server manages a pool of backup media and rotates usage through the pool This ensures that all backups are retained for the administrator specified retention period All media is preformatted with data that allows AMANDA to detect whether or not the proper media is available AMANDA can be interfaced with robotic media changing units, making it possible to completely automate backups See http://www.backupcentral.com/amanda.html Backup 22 11