<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=us-ascii">
<meta name=Generator content="Microsoft Word 12 (filtered medium)">
<style>
<!--
/* Font Definitions */
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.MsoPlainText, li.MsoPlainText, div.MsoPlainText
{mso-style-priority:99;
mso-style-link:"Plain Text Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.5pt;
font-family:Consolas;}
span.PlainTextChar
{mso-style-name:"Plain Text Char";
mso-style-priority:99;
mso-style-link:"Plain Text";
font-family:Consolas;}
.MsoChpDefault
{mso-style-type:export-only;}
@page Section1
{size:8.5in 11.0in;
margin:1.0in 92.4pt 1.0in 92.4pt;}
div.Section1
{page:Section1;}
/* List Definitions */
@list l0
{mso-list-id:919173485;
mso-list-type:hybrid;
mso-list-template-ids:794725460 67698689 67698691 67698693 67698689 67698691 67698693 67698689 67698691 67698693;}
@list l0:level1
{mso-level-number-format:bullet;
mso-level-text:\F0B7;
mso-level-tab-stop:none;
mso-level-number-position:left;
margin-left:.25in;
text-indent:-.25in;
font-family:Symbol;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
-->
</style>
<!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang=EN-US link=blue vlink=purple>
<div class=Section1>
<p class=MsoPlainText>> Sure. Incremental 'dump' sends the whole file,
but upon sending it is</p>
<p class=MsoPlainText>> compressed. Being lots of zeros, the portion of the
stream containing</p>
<p class=MsoPlainText>> the sparse file should still compress well.</p>
<p class=MsoPlainText>> </p>
<p class=MsoPlainText>> Also, assuming the tape is on a tape server,
remember to do the</p>
<p class=MsoPlainText>> compression on the host rather than the tape
server. Something like:</p>
<p class=MsoPlainText>> </p>
<p class=MsoPlainText>> dump | gzip |(netconn) dd</p>
<p class=MsoPlainText>> </p>
<p class=MsoPlainText>> Sending just the changed blocks is quite hard, as
most filesystems</p>
<p class=MsoPlainText>> don't</p>
<p class=MsoPlainText>> know what blocks have changed. But ideally,
the backup system doesn't</p>
<p class=MsoPlainText>> care how the file is represented in blocks, but
merely sees streams</p>
<p class=MsoPlainText>> going on and off tape at its preferred blocksize.</p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><span style='color:black'>So ... again ... yes,
compressing a bunch of zeros brings all the zeros down to near-zero size.
But that's not the goal. Allow me to demonstrate:<o:p></o:p></span></p>
<p class=MsoPlainText><span style='color:black'><o:p> </o:p></span></p>
<p class=MsoPlainText style='margin-left:.25in;text-indent:-.25in;mso-list:
l0 level1 lfo1'><![if !supportLists]><span style='font-family:Symbol;
color:black'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:black'>50G sparse file VMWare
virtual disk, contains Windows XP installation, 22G used.<o:p></o:p></span></p>
<p class=MsoPlainText style='margin-left:.25in;text-indent:-.25in;mso-list:
l0 level1 lfo1'><![if !supportLists]><span style='font-family:Symbol;
color:black'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:black'>Back it up once.
22G go across the network. It takes 30 mins.<o:p></o:p></span></p>
<p class=MsoPlainText style='margin-left:.25in;text-indent:-.25in;mso-list:
l0 level1 lfo1'><![if !supportLists]><span style='font-family:Symbol;
color:black'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:black'>Boot into XP, change a
1K file, shutdown. Including random registry changes and system event
logs and other random changes, imagine that a total of twenty 1k blocks have
changed.<o:p></o:p></span></p>
<p class=MsoPlainText style='margin-left:.25in;text-indent:-.25in;mso-list:
l0 level1 lfo1'><![if !supportLists]><span style='font-family:Symbol;
color:black'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:black'>Now do an incremental
backup. Sure, you may need to scan the file looking for which blocks
changed, but you can do that as fast as you can read the whole file once,
assuming you kept some sort of checksums from the previous time. And then
just send 20k across the net. This should complete at least 5x faster
than before ... which means at most 6 mins.<o:p></o:p></span></p>
<p class=MsoPlainText style='margin-left:.25in;text-indent:-.25in;mso-list:
l0 level1 lfo1'><![if !supportLists]><span style='font-family:Symbol;
color:black'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:black'>If you do this with
tar or dump ... even with compression ... still 22G goes across the net.
Another 30 minute backup.<o:p></o:p></span></p>
<p class=MsoPlainText><span style='color:black'><o:p> </o:p></span></p>
<p class=MsoPlainText><span style='color:black'>Is it clear now?<o:p></o:p></span></p>
</div>
</body>
</html>