do not confuse the reader telling he should use a towers of hanoi

based scheme when it makes no sense: a weekly schedule does not
benefit from it. ok mbalmer@ jmc@ ray@

1 files changed, 30 insertions, 17 deletions

diff --git a/sbin/dump/dump.8 b/sbin/dump/dump.8
index c90caac314a..c0afb2d9433 100644
--- a/sbin/dump/dump.8
+++ b/sbin/dump/dump.8
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: dump.8,v 1.41 2007/05/31 19:19:44 jmc Exp $
+.\"	$OpenBSD: dump.8,v 1.42 2007/11/18 18:56:25 otto Exp $
 .\"	$NetBSD: dump.8,v 1.17 1997/06/05 11:15:06 lukem Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
@@ -31,7 +31,7 @@
 .\"
 .\"     @(#)dump.8	8.1 (Berkeley) 6/16/93
 .\"
-.Dd $Mdocdate: May 31 2007 $
+.Dd $Mdocdate: November 18 2007 $
 .Dt DUMP 8
 .Os
 .Sh NAME
@@ -334,9 +334,9 @@ and will be for some time.
 .Pp
 In the event of a catastrophic disk event, the time required
 to restore all the necessary backup tapes or files to disk
-can be kept to a minimum by staggering the incremental dumps.
-An efficient method of staggering incremental dumps
-to minimize the number of tapes follows:
+is dependent on the levels of the dumps taken.
+A few methods of staggering incremental dumps to either minimize
+backup effort or restore effort follow:
 .Bl -bullet -offset indent
 .It
 Always start with a level 0 backup, for example:
@@ -347,24 +347,37 @@ Always start with a level 0 backup, for example:
 This should be done at set intervals, say once a month or once every two months,
 and on a set of fresh tapes that is saved forever.
 .It
-After a level 0, dumps of active file
-systems are taken on a daily basis,
-using a modified Tower of Hanoi algorithm,
-with this sequence of dump levels:
+After the level 0 dump,
+backups of active file systems are taken on each day in a cycle of a week.
+Once a week, a level 1 dump is taken.
+The other days of the week a higher level dump is done.
+.Pp
+The following cycle needs at most three tapes to restore to a given point
+in time,
+but the dumps at the end of the weekly cycle will require more
+time and space:
 .Bd -literal -offset indent
-3 2 5 4 7 6 9 8 9 9 ...
+1 2 2 2 2 2 2
 .Ed
 .Pp
-For the daily dumps, it should be possible to use a fixed number of tapes
-for each day, used on a weekly basis.
-Each week, a level 1 dump is taken, and
-the daily Hanoi sequence repeats beginning with 3.
-For weekly dumps, another fixed set of tapes per dumped file system is
-used, also on a cyclical basis.
-.El
+This sequence requires at most eight tapes to restore,
+but the size of the individual dumps will be smaller:
+.Bd -literal -offset indent
+1 2 3 4 5 6 7
+.Ed
 .Pp
+This sequence seeks a compromise between backup and restore effort:
+.Bd -literal -offset indent
+1 2 2 3 3 4 4
+.Ed
+.Pp
+The weekly level 1 dumps should be done on a set of tapes that
+is used cyclically.
+For the daily dumps a tape per day of the week can be used.
+.It
 After several months or so, the daily and weekly tapes should get
 rotated out of the dump cycle and fresh tapes brought in.
+.El
 .Pp
 If
 .Nm