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+<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN">
+<HTML
+><HEAD
+><TITLE
+>Multilevel backups</TITLE
+><META
+NAME="GENERATOR"
+CONTENT="Modular DocBook HTML Stylesheet"><LINK
+REL="HOME"
+TITLE="The Linux System Administrators' Guide"
+HREF="book1.html"><LINK
+REL="UP"
+TITLE="Backups"
+HREF="c2187.html"><LINK
+REL="PREVIOUS"
+TITLE="Simple backups"
+HREF="x2240.html"><LINK
+REL="NEXT"
+TITLE="What to back up"
+HREF="x2405.html"></HEAD
+><BODY
+BGCOLOR="#FFFFFF"
+TEXT="#000000"
+><DIV
+CLASS="NAVHEADER"
+><TABLE
+WIDTH="100%"
+BORDER="0"
+CELLPADDING="0"
+CELLSPACING="0"
+><TR
+><TH
+COLSPAN="3"
+ALIGN="center"
+>The Linux System Administrators' Guide</TH
+></TR
+><TR
+><TD
+WIDTH="10%"
+ALIGN="left"
+VALIGN="bottom"
+><A
+HREF="x2240.html"
+>Prev</A
+></TD
+><TD
+WIDTH="80%"
+ALIGN="center"
+VALIGN="bottom"
+>Chapter 10. Backups</TD
+><TD
+WIDTH="10%"
+ALIGN="right"
+VALIGN="bottom"
+><A
+HREF="x2405.html"
+>Next</A
+></TD
+></TR
+></TABLE
+><HR
+ALIGN="LEFT"
+WIDTH="100%"></DIV
+><DIV
+CLASS="SECT1"
+><H1
+CLASS="SECT1"
+><A
+NAME="AEN2315"
+>Multilevel backups</A
+></H1
+><P
+> The simple backup method outlined in the previous section
+	is often quite adequate for personal use or small sites.  For more
+	heavy duty use, multilevel backups are more appropriate.  </P
+><P
+> The simple method has two backup levels: full and
+	incremental backups.  This can be generalized to any number of
+	levels.  A full backup would be level 0, and the different levels
+	of incremental backups levels 1, 2, 3, etc.  At each incremental
+	backup level you back up everything that has changed since the
+	previous backup at the same or a previous level.  </P
+><P
+> The purpose for doing this is that it allows a longer
+	<I
+CLASS="GLOSSTERM"
+>backup history</I
+> cheaply.	In the example in
+	the previous section, the backup history went back to the previous
+	full backup.  This could be extended by having more tapes, but
+	only a week per new tape, which might be too expensive.  A longer
+	backup history is useful, since deleted or corrupted files are
+	often not noticed for a long time.  Even a version of a file that
+	is not very up to date is better than no file at all.  </P
+><P
+> With multiple levels the backup history can be extended
+	more cheaply.  For example, if we buy ten tapes, we could use
+	tapes 1 and 2 for monthly backups (first Friday each month),
+	tapes 3 to 6 for weekly backups (other Fridays; note that there
+	can be five Fridays in one month, so we need four more tapes),
+	and tapes 7 to 10 for daily backups (Monday to Thursday).
+	With only four more tapes, we've been able to extend the backup
+	history from two weeks (after all daily tapes have been used)
+	to two months.	It is true that we can't restore every version
+	of each file during those two months, but what we can restore
+	is often good enough.  </P
+><P
+><A
+HREF="x2315.html#BACKUP-HISTORY-TIMELINE"
+>Figure 10-1</A
+> shows which backup
+	level is used each day, and which backups can be restored from
+	at the end of the month.  </P
+><DIV
+CLASS="FIGURE"
+><P
+><B
+><A
+NAME="BACKUP-HISTORY-TIMELINE"
+>Figure 10-1. A sample multilevel backup schedule.</A
+></B
+></P
+><P
+><IMG
+SRC="backup-timeline.gif"></P
+></DIV
+><P
+> Backup levels can also be used to keep filesystem
+	restoration time to a minimum.	If you have many incremental
+	backups with monotonously growing level numbers, you need to
+	restore all of them if you need to rebuild the whole filesystem.
+	Instead you can use level numbers that aren't monotonous, and
+	keep down the number of backups to restore.  </P
+><P
+> To minimize the number of tapes needed to restore, you
+	could use a smaller level for each incremental tape.  However,
+	then the time to make the backups increases (each backup copies
+	everything since the previous full backup).  A better scheme is
+	suggested by the <B
+CLASS="COMMAND"
+>dump</B
+> manual page and described
+	by the table XX (efficient-backup-levels).  Use the following
+	succession of backup levels: 3, 2, 5, 4, 7, 6, 9, 8, 9, etc.
+	This keeps both the backup and restore times low.  The most you
+	have to backup is two day's worth of work.  The number of tapes
+	for a restore depends on how long you keep between full backups,
+	but it is less than in the simple schemes.  </P
+><DIV
+CLASS="TABLE"
+><P
+><B
+><A
+NAME="EFFICIENT-BACKUP-LEVELS"
+>Table 10-1. Efficient backup scheme using many backup levels</A
+></B
+></P
+><TABLE
+BORDER="1"
+CLASS="CALSTABLE"
+><TR
+><TH
+ALIGN="LEFT"
+VALIGN="TOP"
+>Tape</TH
+><TH
+ALIGN="LEFT"
+VALIGN="TOP"
+>Level</TH
+><TH
+ALIGN="LEFT"
+VALIGN="TOP"
+>Backup (days)</TH
+><TH
+ALIGN="LEFT"
+VALIGN="TOP"
+>Restore tapes</TH
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>0</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>n/a</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>2</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>3</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>3</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>2</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>2</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 3</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>4</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>5</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 4</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>5</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>4</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>2</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>6</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>7</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 6</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>7</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>6</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>2</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 7</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>8</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>9</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 7, 8</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>9</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>8</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>2</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 7, 9</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>10</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>9</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 7, 9, 10</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>11</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>9</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 7, 9, 10, 11</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>...</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>9</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>1, 2, 5, 7, 9, 10, 11, ...</TD
+></TR
+></TABLE
+></DIV
+><P
+> A fancy scheme can reduce the amount of labor needed, but
+	it does mean there are more things to keep track of.  You must
+	decide if it is worth it.  </P
+><P
+> <B
+CLASS="COMMAND"
+>dump</B
+> has built-in support for backup
+	levels.  For <B
+CLASS="COMMAND"
+>tar</B
+> and <B
+CLASS="COMMAND"
+>cpio</B
+>
+	it must be implemented with shell scripts.  </P
+></DIV
+><DIV
+CLASS="NAVFOOTER"
+><HR
+ALIGN="LEFT"
+WIDTH="100%"><TABLE
+WIDTH="100%"
+BORDER="0"
+CELLPADDING="0"
+CELLSPACING="0"
+><TR
+><TD
+WIDTH="33%"
+ALIGN="left"
+VALIGN="top"
+><A
+HREF="x2240.html"
+>Prev</A
+></TD
+><TD
+WIDTH="34%"
+ALIGN="center"
+VALIGN="top"
+><A
+HREF="book1.html"
+>Home</A
+></TD
+><TD
+WIDTH="33%"
+ALIGN="right"
+VALIGN="top"
+><A
+HREF="x2405.html"
+>Next</A
+></TD
+></TR
+><TR
+><TD
+WIDTH="33%"
+ALIGN="left"
+VALIGN="top"
+>Simple backups</TD
+><TD
+WIDTH="34%"
+ALIGN="center"
+VALIGN="top"
+><A
+HREF="c2187.html"
+>Up</A
+></TD
+><TD
+WIDTH="33%"
+ALIGN="right"
+VALIGN="top"
+>What to back up</TD
+></TR
+></TABLE
+></DIV
+></BODY
+></HTML
+>
+\ No newline at end of file