diff options
Diffstat (limited to 'sag-0.6.1-www/Invisible/sag-0.6/node105.html')
| -rw-r--r-- | sag-0.6.1-www/Invisible/sag-0.6/node105.html | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node105.html b/sag-0.6.1-www/Invisible/sag-0.6/node105.html new file mode 100644 index 0000000..89f5c84 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node105.html @@ -0,0 +1,57 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Compressed backups</TITLE> +<META NAME="description" CONTENT="Compressed backups"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html1635" HREF="node106.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1633" HREF="node96.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1629" HREF="node104.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1637" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1638" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1636" HREF="node106.html">Keeping Time</A> +<B>Up:</B> <A NAME="tex2html1634" HREF="node96.html">Backups</A> +<B> Previous:</B> <A NAME="tex2html1630" HREF="node104.html">What to back up</A> +<BR> <P> +<H1><A NAME="SECTION001170000000000000000">Compressed backups</A></H1> +<P> + Backups take a lot of space, which can cost quite a lot of money. + To reduce the space needed, the backups can be compressed. There + are several ways of doing this. Some programs have support for + for compression built in; for example, the <tt>-gzip</tt> (<tt>-z</tt>) + option for GNU <tt>tar</tt><A NAME="3099"> </A> pipes the whole backup through the + <tt>gzip</tt><A NAME="3101"> </A> compression program, before writing it to the backup + medium. +<P> + Unfortunately, compressed backups can cause trouble. Due to the + nature of how compression works, if a single bit is + wrong, all the rest of the compressed data will be unusable. Some + backup programs have some built in error correction, but no method + can handle a large number of errors. This means that if the + backup is compressed the way GNU <tt>tar</tt><A NAME="3103"> </A> does it, with the + whole output compressed as a unit, a single error makes all the + rest of the backup lost. Backups must be reliable, and this + method of compression is not a good idea. +<P> + An alternative way is to compress each file separately. This still + means that the one file is lost, but all other files are unharmed. + The lost file would have been corrupted anyway, so this situation + is not much worse than not using compression at all. The <tt>afio</tt><A NAME="3105"> </A> + program (a variant of <tt>cpio</tt><A NAME="3107"> </A>) can do this. +<P> + Compression takes some time, which may make the backup program + unable to write data fast enough for a tape drive.<A NAME="tex2html52" HREF="footnode.html#3016"><IMG ALIGN=BOTTOM ALT="gif" SRC="./foot_motif.gif"></A> This can be + avoided by buffering the output (either internally, if the backup + program if smart enough, or by using another program), but even that + might not work well enough. This should only be a problem on slow + computers. +<P> +<BR> <HR> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |