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>From: Geoff Hazel <geoff_hazel AT yahoo DOT com>
>Subject: [Veritas-bu] Why don't tapes hold the same amount of data?
>
>We have all the same tapes in the robot library, but when I look at the 
"full" tapes I see a wide difference in the >amount of data they have:
> 
>  A00085  HCART    TLD      0       16     -       3     151715893 FULL
>A00088  HCART    TLD      0       7      -       1     255478199 FULL
>A00089  HCART    TLD      0       10     -       1     343680501 FULL
>A00090  HCART    TLD      0       13     -       3     315433835 FULL
>
>  Why do some tapes hold twice as much data as other tapes?

Goeff,

You have to look at the data that is being backed up.  When you write to 
tape, the data is most likely being compressed.  Not all data compresses 
the same amount.  I have seen 8 GB databases compress down to about 8 MB 
of tape space, and I have seen some compressed files actually increase in 
size when written to tape.  Unfortunately, I do not think NetBackup keeps 
track of that.

Richard Mickle
UNIX Systems and Storage Administrator
Moore Wallace Response Marketing Services
An RR Donnelley Company
E-Mail:         Richard.Mickle AT mwrms.rrd DOT com
Phone:        920-339-1695
Cell Phone: 920-366-1987
Fax:             920-339-1807

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<br><font size=2><tt>&gt;From: Geoff Hazel &lt;geoff_hazel AT yahoo DOT 
com&gt;<br>
&gt;Subject: [Veritas-bu] Why don't tapes hold the same amount of data?<br>
&gt;<br>
&gt;We have all the same tapes in the robot library, but when I look at
the &quot;full&quot; tapes I see a wide difference in the &gt;amount of
data they have:<br>
&gt; &nbsp; <br>
&gt; &nbsp;A00085 &nbsp;HCART &nbsp; &nbsp;TLD &nbsp; &nbsp; &nbsp;0 &nbsp;
&nbsp; &nbsp; 16 &nbsp; &nbsp; - &nbsp; &nbsp; &nbsp; 3 &nbsp; &nbsp; 151715893
&nbsp; &nbsp; &nbsp; &nbsp;FULL<br>
&gt;A00088 &nbsp;HCART &nbsp; &nbsp;TLD &nbsp; &nbsp; &nbsp;0 &nbsp; &nbsp;
&nbsp; 7 &nbsp; &nbsp; &nbsp;- &nbsp; &nbsp; &nbsp; 1 &nbsp; &nbsp; 255478199
&nbsp; &nbsp; &nbsp; &nbsp;FULL<br>
&gt;A00089 &nbsp;HCART &nbsp; &nbsp;TLD &nbsp; &nbsp; &nbsp;0 &nbsp; &nbsp;
&nbsp; 10 &nbsp; &nbsp; - &nbsp; &nbsp; &nbsp; 1 &nbsp; &nbsp; 343680501
&nbsp; &nbsp; &nbsp; &nbsp;FULL<br>
&gt;A00090 &nbsp;HCART &nbsp; &nbsp;TLD &nbsp; &nbsp; &nbsp;0 &nbsp; &nbsp;
&nbsp; 13 &nbsp; &nbsp; - &nbsp; &nbsp; &nbsp; 3 &nbsp; &nbsp; 315433835
&nbsp; &nbsp; &nbsp; &nbsp;FULL<br>
&gt;<br>
&gt; &nbsp;Why do some tapes hold twice as much data as other tapes?<br>
</tt></font>
<br><font size=2 face="sans-serif">Goeff,</font>
<br>
<br><font size=2 face="sans-serif">You have to look at the data that is
being backed up. &nbsp;When you write to tape, the data is most likely
being compressed. &nbsp;Not all data compresses the same amount. &nbsp;I
have seen 8 GB databases compress down to about 8 MB of tape space, and
I have seen some compressed files actually increase in size when written
to tape. &nbsp;Unfortunately, I do not think NetBackup keeps track of 
that.</font>
<br><font size=2 face="sans-serif"><br>
Richard Mickle<br>
UNIX Systems and Storage Administrator<br>
Moore Wallace Response Marketing Services<br>
An RR Donnelley Company<br>
E-Mail: &nbsp; &nbsp; &nbsp; &nbsp; Richard.Mickle AT mwrms.rrd DOT com<br>
Phone: &nbsp; &nbsp; &nbsp; &nbsp;920-339-1695<br>
Cell Phone: 920-366-1987<br>
Fax: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 920-339-1807<br>
</font>
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