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Why is my differencing disk so big?

Source: microsoft.public.virtualpc
Sent: 06/25/2008
From: JasBro
Message:

I have a vhd with XP, Oracle 10, Tomcat 6, Java6. It contains an Oracle DB
instance with a bunch of tablespace files, but no data in the db.
Uncompressed, this disk is about 6.5GB

I create a differencing disk off of that base and a virtual machine using
the differencing disk. In that disk I create a user in the Oracle DB, create
a few tables and add a little data. I also create a webapp under Tomcat. My
differencing disk is 5.5GB.

Is this because the tablespace files are getting completely copied to the
differencing disk? Put another way, does the differencing disk get a
complete copy of the changed file, or just a "difference between" similar to
SCCS source control on Unix?

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Related Messages

Re: Why is my differencing disk so big?

Sent: 06/26/2008
From: Bo Berglund <(email address - cut out)>
Message:

On Wed, 25 Jun 2008 13:22:05 -0700, JasBro
<(email address - cut out)> wrote:

Not an expert, but what I believe differencing disks do for you is
this:
- Base any number of new guests on one configured and working guest
- The base VHD is *never* written to so it can be set readonly
- *All* data you ever save in a derived guest go to the diff VHD disk
file and this includes the Windows swap file....

This means that the differencing disk will expand depending on how
your applications write data to it.

Now, the crucial question is to what extent the applications do change
the data and here I don't know. But a database server is likely to
change the contents of its files and in the case of MSSQLServer this
means the mdf and the ldf files (since these are normally the only two
files in a database irrespective of the number of tables). Other
database engines spread their tables into separate files. What Oracle
does I don't know.

--

Bo Berglund (Sweden)

Show quoted text

>I have a vhd with XP, Oracle 10, Tomcat 6, Java6. It contains an Oracle DB
>instance with a bunch of tablespace files, but no data in the db.
>Uncompressed, this disk is about 6.5GB
>
>I create a differencing disk off of that base and a virtual machine using
>the differencing disk. In that disk I create a user in the Oracle DB, create
>a few tables and add a little data. I also create a webapp under Tomcat. My
>differencing disk is 5.5GB.
>
>Is this because the tablespace files are getting completely copied to the
>differencing disk? Put another way, does the differencing disk get a
>complete copy of the changed file, or just a "difference between" similar to
>SCCS source control on Unix?

Post Reply | This is Spam! | Mark as Spam

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