diff --git a/en_US.ISO8859-1/books/handbook/disks/chapter.xml b/en_US.ISO8859-1/books/handbook/disks/chapter.xml index 3fbe5fa785..3f70eacfb1 100644 --- a/en_US.ISO8859-1/books/handbook/disks/chapter.xml +++ b/en_US.ISO8859-1/books/handbook/disks/chapter.xml @@ -1576,11 +1576,11 @@ cd0: Attempt to query device size failed: NOT READY, Medium not present - tray c - - - Backup Strategies + + Backup Basics - + - The first requirement in devising a backup plan is to make - sure that all of the following problems are covered: + Implementing a backup plan is essential in order to have the + ability to recover from disk failure, accidental file deletion, + random file corruption, or complete machine destruction, + including destruction of on-site backups. - - - Disk failure. - - - - Accidental file deletion. - - - - Random file corruption. - - - - Complete machine destruction, say by fire, including - destruction of any on-site backups. - - - - Some systems will be best served by having each of these - problems covered by a completely different technique. Except - for strictly personal systems with low-value data, it is - unlikely that one technique will cover all of them. - - Some possible techniques include: + The backup type and schedule will vary, depending upon the + importance of the data, the granularity needed for file + restores, and the amount of acceptable downtime. Some possible + backup techniques include: Archives of the whole system, backed up onto permanent, off-site media. This provides protection against all of the problems listed above, but is slow and inconvenient to - restore from. Copies of the backups can be stored on site - or online, but there will still be inconveniences in - restoring files, especially for non-privileged users. + restore from, especially for non-privileged users. - Filesystem snapshots, which are really only helpful in - the accidental file deletion scenario, but can be - very helpful in that case, as well as - quick and easy to deal with. + Filesystem snapshots, which are useful for restoring + deleted files or previous versions of files. - Copies of whole file systems or disks which can be - created with a periodic net/rsync of the - whole machine. This is generally most useful in networks - with unique requirements. For general protection against - disk failure, this is usually inferior to - RAID. For restoring accidentally deleted - files, it can be comparable to UFS - snapshots. + Copies of whole file systems or disks which are + sychronized with another system on the network using a + scheduled net/rsync. - RAID, which minimizes or avoids - downtime when a disk fails at the expense of having to deal - with disk failures more often, because there are more disks, - albeit at a much lower urgency. - - - - Checking fingerprints of files using &man.mtree.8;. - Although this is not a backup, this technique indicates - when one needs to resort to backups. This is particularly - important for offline backups, and should be checked - periodically. + Hardware or software RAID, which minimizes or avoids + downtime when a disk fails. - It is quite easy to come up with more techniques, many - of them variations on the ones listed above. Specialized - requirements usually lead to specialized techniques. For - example, backing up a live database usually requires a method - particular to the database software as an intermediate step. - The important thing is to know which dangers should be protected - against, and how each will be handled. - - - - Backup Basics - - The major backup programs built into &os; are - &man.dump.8;, &man.tar.1;, &man.cpio.1;, and - &man.pax.1;. + Typically, a mix of backup techniques is used. For + example, one could create a schedule to automate a weekly, full + system backup that is stored off-site and to supplement this + backup with hourly ZFS snapshots. In addition, one could make a + manual backup of individual directories or files before making + file edits or deletions. + + This section describes some of the utilities which can be + used to create and manage backups on a &os; system. - Dump and Restore + File System Backups backup software @@ -1773,13 +1729,16 @@ cd0: Attempt to query device size failed: NOT READY, Medium not present - tray c - <command>tar</command> + Directory Backups backup software tar + Several built-in utilities are available for backing up + and restoring specified files and directories as needed. + &man.tar.1; also dates back to Version 6 of AT&T &unix;, circa 1975. tar operates in cooperation with the file system and writes files and @@ -1798,10 +1757,6 @@ cd0: Attempt to query device size failed: NOT READY, Medium not present - tray c When backing up over an insecure network, instead use ssh. - - - - <command>cpio</command> backup software @@ -1837,10 +1792,6 @@ cd0: Attempt to query device size failed: NOT READY, Medium not present - tray c backups, and backup_device is where the backups should be written to, such as /dev/nsa0). - - - - <command>pax</command> backup software @@ -1904,56 +1855,6 @@ cd0: Attempt to query device size failed: NOT READY, Medium not present - tray c but is available as either a port or package. - - Do Nothing - - Do nothing is not a computer program, but - it is the most widely used backup strategy. There are no - initial costs. There is no backup schedule to follow. Just - say no. If something happens to your data, grin and bear - it! - - If your time and data is worth little to nothing, then - Do nothing is the most suitable backup program - for the computer. But beware, &os; is a useful tool and - over time it can be used to create a valuable collection of - files. - - Do nothing is the correct backup method for - /usr/obj and other - directory trees that can be exactly recreated by the computer. - An example is the files that comprise the HTML or &postscript; - version of this Handbook. These document formats have been - created from XML input files. Creating backups of the HTML or - &postscript; files is not necessary if the XML files are - backed up regularly. - - - - Which Backup Program Is Best? - - - LISA - - - &man.dump.8; Period. Elizabeth D. - Zwicky torture tested all the backup programs discussed here. - The clear choice for preserving all your data and all the - peculiarities of &unix; file systems is - dump. Elizabeth created file systems - containing a large variety of unusual conditions (and some not - so unusual ones) and tested each program by doing a backup and - restore of those file systems. The peculiarities included: - files with holes, files with holes and a block of nulls, files - with funny characters in their names, unreadable and - unwritable files, devices, files that change size during the - backup, files that are created/deleted during the backup and - more. She presented the results at LISA V in Oct. 1991. See - torture-testing - Backup and Archive Programs. - - Emergency Restore Procedure