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<h2 class="style1">Volume Shadow Service</h2>
<p>Cobian Backup 9 can now copy files that are in exclusive use by
other applications. It does so by using Volume Shadow Services, a
technology that is present on Windows XP or a newer MS operative
system.<h2>What is Volume Shadow Copy Service?</h2>
<p>VSS is a mechanism for creating consistent point-in-time copies
of data known as shadow copies. The Volume Shadow Copy Service can
produce consistent shadow copies by coordinating with business
applications, file-system services, backup applications, fast
recovery solutions, and storage hardware.
<p>The Volume Shadow Copy Service is commonly used in the following
scenarios:
<p><span class="style2">Consistent backups of open files and
applications</span>: Applications that are running often keep their
files open continuously. For backup, this can present a problem
because this prevents backup applications from accessing and copying
these files to backup media. Even if an application does not have
its files open, it is possible because of the finite time needed to
open, back up, and close a file that files copied to the backup
media might not all reflect the same application state at the same
point in time.<p>Additionally,<span class="style2"> backing up
servers that are running critical applications </span>such as
databases or messaging services presents a unique challenge. These
applications run in a volatile state as a result of extensive
optimizations that deal with huge flows of transactions and
messages. Because these applications keep their data in a constant
flux between memory and disk, it is difficult to pinpoint the data
that needs to be archived.
<p>The most straightforward solution is to interrupt the application
during backup, which puts the data into a stable state, but might
result in unacceptable amounts of downtime, particularly if the
applications are large.
<p>For both problems, the Volume Shadow Copy Service provides a
solution by enabling a snapshot of the data at a given point in
time, while minimizing the interruption to applications. This can
involve cooperation from the applications, so that they can notify
the operating system that they are briefly quiescing their data for
archival. During quiescence, applications make data on the disk
consistent. For example, an application might flush its buffers to
disk or write out in-memory data to disk.
<h2>Considerations</h2>
<p>To be able to use VSS you need to install and run the program on
Windows XP, 2002, Vista or newer. <p>Because the program needs to
create a snapshot of the volume data before the backup begins, using
VSS is slower than a normal backup. You will need also a lot of
extra free space for the system to be able to create the snapshot.
That's why, you may want to not use VSS if there is no need to. If
you know that the files that you are going to backup will not be
locked when the backup begins, it's a lot more efficient to copy
directly.<p>You can use VSS for local volumes, so a remote volume
will not be able to use VSS and will always be copied
directly.<p>Be aware that the
account that is running the backup may need <span class="style2">
administrative or backup operator privileges</span> to create a VSS
snapshot.<p>The Shadow Copy will <span class="style2">always be created by the original
user that is running the engine</span> and not by the user that is
impersonated (if impersonation is used)<p>The Shell method cannot be used with VSS!<p>Please see the <a href="faq_en.htm">FAQ</a> for other
questions related to VSS.<p> <p class="style1">
<a href="index_en.htm">Index</a></td>
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<p class="style1">⌐2000-2008 by Luis Cobian<br>
All rights reserved</td>
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