Chapter 11 Backups Honglin Su CSEE UMBC hosu cs

Chapter 11, Backups Honglin Su CSEE, UMBC hosu@cs. umbc. edu CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 1

Agenda • • Introduction Backup Devices and Media Incremental Backup Rules Restoring from Dumps Dumping and Restoring from Upgrades Other Archiving Programs Summary CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 2

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 3

Backup Devices and Media CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 4

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 5

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 6

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 7

Incremental Backup Solaris Maintenance Commands Linux ufsdump(1 M) DUMP(8) UNIX System Manager's Manual NAME ufsdump - incremental file system dump NAME dump - filesystem backup SYNOPSIS /usr/sbin/ufsdump [options] [arguments] files_to_dump DUMP(8) SYNOPSIS dump [0123456789 Bbhfus. Td. Wn [argument. . . ]] filesystem dump [0123456789 Bbhfus. Td. Wn [argument. . . ]] directory DESCRIPTION ufsdump backs up all files specified by files_to_dump (normally either a whole file system or files within a file system changed after a certain date) to magnetic tape, diskette, or disk file. When running ufsdump, the file system must be inactive; otherwise, the output of ufsdump may be inconsistent and restoring files correctly may be impossible. A file system is inactive when it is unmouned or the system is in single user mode. A file system is not considered inactive if one tree of the file system is quiescent while another tree has files or directories being modified. CMSC 691 X, Summer 1999 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 storage 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. Honglin Su, CSEE UMBC 8

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. CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 9

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 10

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 11

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 12

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 CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 13

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. CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 14

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/rmt 0 of=/dev/rmt 1 cbs=16 b • volcopy: Duplicate Filesystems CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 15

Other Archiving Programs User Commands • tar(1) NAME tar - create tape archives and add or extract files SYNOPSIS tar c [b. Bef. Fhiklnop. Pqvw. X [ 0 -7 ]] [ block ] [ tarfile ] [ exclude-file ] { -I include-file | -C directory file | file }. . . tar r [ b. Bef. Fhiklnqvw [ 0 -7 ]] [ block ] { -I include-file | -C directory file | file }. . . tar t [ Bef. Fhiklnqv. X [ 0 -7 ]] [ tarfile ] [ exclude-file ] { -I include-file | file }. . . tar u [ b. Bef. Fhiklnqvw [ 0 -7 ]] [ block ] [ tarfile ] file. . . actaeon. cs. umbc. edu[130] tar cvf tmp. tar tmp a tmp/ 0 K a tmp/yt. hm 12 K a tmp/review 1. txt 2 K a tmp/email 2 K a tmp/Map. ppt 31 K a tmp/bob. c 1 K actaeon. cs. umbc. edu[132] tar xvf tmp. tar x tmp, 0 bytes, 0 tape blocks x tmp/yt. hm, 11360 bytes, 23 tape blocks x tmp/review 1. txt, 1163 bytes, 3 tape blocks x tmp/email, 1201 bytes, 3 tape blocks x tmp/Map. ppt, 31232 bytes, 61 tape blocks x tmp/bob. c, 61 bytes, 1 tape blocks tar x [ Bef. Fhiklmnopqvw. X [ 0 -7 ]] [ tarfile ] [ exclude-file ] [ file. . . ] CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 16

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] mt usage: mt [ -f device ] command [ count ] CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 17

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! CMSC 691 X, Summer 1999 Honglin Su, CSEE UMBC 18