cmsc 691x, summer 1999 honglin su, csee umbc1 chapter 11, backups honglin su csee, umbc...
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CMSC 691X, Summer 1999
Honglin Su, CSEE UMBC 1
Chapter 11, Backups
Honglin Su
CSEE, UMBC
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CMSC 691X, Summer 1999
Honglin Su, CSEE UMBC 2
Agenda
• Introduction• Backup Devices and Media• Incremental Backup• Backup Rules• Restoring from Dumps• Dumping and Restoring from Upgrades• Other Archiving Programs• Summary
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Introduction
• Information stored on computers is worth more than the computers themselves– Consider your accounts stored in Banks
• Hundreds of ways to lose data.– Accidental file removal, External/Internal failures
• Backup - The most efficient and convenient way to protect your data
• Backup must be done carefully and on a strict schedule
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Backup Devices and MediaMedium Capacity Cost Cost/MB Type Reuse Random
FloppyDisk
2.8 MB $0.5 17.60 c M Yes Yes
QIC 150 MB $20 13.30 c M Yes No
Nine-track
160 MB $10 6.25 c M Yes No
Floptical 200 MB $15 7.50 c M/O Yes Yes
WCD-ROM
600MB $10 1.67 c B/O No Yes
Exabyte(8mm)
5 GB+ $9 <0.18 c M Yes No
DAT(4mm)
5 GB+ $7 <0.14 c M Yes No
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Backup Devices and Media
• Most media use magnetic particles to store their data, these media are subject to damage by electrical and magnetic fields.
• New Trends– Larger capacity devices, such as Tape libraries, using
robot; others, e.g. Jukeboxes and Stackers
– Higher speed: 12 MB/s
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Incremental Backup
• dump: builds a list of files that have been modified since a previous dump, then packs those files into a single large file to archive to an external device.– Backups can span multiple tapes
– Files of any type (even devices) can be backed up and restored
– Permission, ownerships, and modify times can be restored
– Files with holes are handled correctly
– Backups can be performed incrementally
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Incremental Backup
• Limitation of dump: – Every filesystem must be dumped individually
• If you have a disk that is partitioned , you must dump each section of the disk separately
– The other limitation is that only filesystems on the local machine can be dumped
• You can not dump an NFS filesystem, however, rdump can dump a local filesystem to a remote tape drive
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Incremental Backup
Maintenance Commands ufsdump(1M) NAME ufsdump - incremental file system dump SYNOPSIS /usr/sbin/ufsdump [options] [arguments] files_to_dump DESCRIPTION ufsdump backs up all files specified by files_to_dump (nor- mally either a whole file system or files within a file sys- tem changed after a certain date) to magnetic tape, diskette, or disk file. When running ufsdump, the file sys- tem must be inactive; otherwise, the output of ufsdump may be inconsistent and restoring files correctly may be impos- sible. A file system is inactive when it is unmouned or the system is in single user mode. A file system is not con- sidered inactive if one tree of the file system is quiescent while another tree has files or directories being modified.
Solaris LinuxDUMP(8) UNIX System Manager's Manual DUMP(8) NAME dump - filesystem backup SYNOPSIS dump [0123456789BbhfusTdWn [argument ...]] filesystem dump [0123456789BbhfusTdWn [argument ...]] directory DESCRIPTION Dump examines files on a filesystem and determines which files need to be backed up. These files are copied to the given disk, tape or other stor- age medium for safe keeping (see the f option below for doing remote backups). A dump that is larger than the output medium is broken into multiple volumes. On most media the size is determined by writing until an end-of-media indication is returned. On media that cannot reliably return an end-of-media indication (such as some cartridge tape drives) each volume is of a fixed size; the actual size is determined by the tape size and density and/or block count options below. By default, the same output file name is used for each volume after prompting the operator to change media.
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Incremental Backup
• Backup level 0 ~ 9– A level zero backup places the entire filesystem on the
tape
– A level N dump backs up all files that have changed since the last dump level less than N.
– To restore files from several sets of backup tapes to reset a filesystem to its exact state during the last backup.
• dump does not care about the length of filename.
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Incremental Backup
• Dump sequences and schedule– The schedule that is right for you depends on
• The activity of your filesystems
• The capacity of your dump device
• The amount of redundance you want
• The number of tapes you want to buy
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Backup Rules
• Perform all dumps from one machine– using rdump, there is a performance penalty, while the
ease of administration makes it worthwhile.
• Label your tapes: exalabel• Pick a reasonable backup interval
– The more often backups are done, the smaller the amount of data that can be lost in a crash
• Choose filesystems carefully
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Backup Rules
• Make daily dumps fit on one tape• Make filesystems samller than your dump device• Keep tapes off-site• Limit Activity during dumps• Check your tapes
– Verify that the tape contains the expected files
• Prepare for the worst
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Restoring from Dumps
• Restoring individual files– restore x filename
– use rrestore to extract files from rdump.
– If multiple files on a single tape, use mt to position the tape at the correct dump file before running restore
• Interactive restore– If your version of restore supports the i option.
• Restore entire filesystems– restore r
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Dumping and Restoring for Upgrades
• When you perform an OS upgrade, all filesystems must be backed up with a level zero dump.
• Be sure to back up and restore any system-specific files that are in / or /usr, such as /etc/passwd, /usr/local, etc.
• Your should do a complete set of level zero dumps immediately after an upgrade.
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Other Archiving Programs
• tar: Package Files• cpio: ATT-ish Archiving, copy file archives in and
out, similar to tar• dd: Twiddle Bits
– % dd if=/dev/rmt0 of=/dev/rmt1 cbs=16b
• volcopy: Duplicate Filesystems
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Other Archiving Programs
• tarUser Commands tar(1) NAME tar - create tape archives and add or extract files SYNOPSIS tar c [bBefFhiklnopPqvwX [ 0-7 ]] [ block ] [ tarfile ] [ exclude-file ] { -I include-file | -C directory file | file } ... tar r [ bBefFhiklnqvw [ 0-7 ]] [ block ] { -I include-file | -C directory file | file } ... tar t [ BefFhiklnqvX [ 0-7 ]] [ tarfile ] [ exclude-file ] { -I include-file | file } ... tar u [ bBefFhiklnqvw [ 0-7 ]] [ block ] [ tarfile ] file ... tar x [ BefFhiklmnopqvwX [ 0-7 ]] [ tarfile ] [ exclude-file ] [ file ... ]
actaeon.cs.umbc.edu[130] tar cvf tmp.tar tmpa tmp/ 0Ka tmp/yt.hm 12Ka tmp/review1.txt 2Ka tmp/email 2Ka tmp/Map.ppt 31Ka tmp/bob.c 1Kactaeon.cs.umbc.edu[132] tar xvf tmp.tarx tmp, 0 bytes, 0 tape blocksx tmp/yt.hm, 11360 bytes, 23 tape blocksx tmp/review1.txt, 1163 bytes, 3 tape blocksx tmp/email, 1201 bytes, 3 tape blocksx tmp/Map.ppt, 31232 bytes, 61 tape blocksx tmp/bob.c, 61 bytes, 1 tape blocks
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Using multiple files on a single tape
• mt command– rew - rewind the tape to the beginning
– offl - put the tape off-line
– status - show the status of the tape drive
– fsf [count] - fast-forwards the tape
– bsf [count] - backspace count files
actaeon.cs.umbc.edu[137] mtusage: mt [ -f device ] command [ count ]
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Summary
• Related chapters– Chapter 4, The filesystem
– Chapter 7, Devices and drivers
– Chapter 9, Adding a disk
– Chapter 10, Periodic Processes
– Chapter 17, NFS
• For more information– http://www.admin.com/
– http://wwwhost.cc.utexas.edu/cc/services/unix/index.html
• Q & A
• Thank you!