187 lines
4.2 KiB
HTML
187 lines
4.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Creating snapshot objects</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="EVMS User Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Creating snapshots"
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HREF="evmscreatesnap.html"><LINK
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REL="PREVIOUS"
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TITLE="What is a snapshot?"
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HREF="whatissnapshotting.html"><LINK
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REL="NEXT"
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TITLE="Example: create a snapshot"
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HREF="snapshotex.html"></HEAD
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>Prev</A
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 11. Creating snapshots</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="snapshotex.html"
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>Next</A
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><H1
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CLASS="sect1"
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><A
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NAME="createactivsnap"
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></A
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>11.2. Creating snapshot objects</H1
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><P
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>You can create a snapshot object from any unused storage object in EVMS
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(disks, segments, regions, or feature objects).
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The size of this consumed object is
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the size available to the snapshot object. The snapshot object can be smaller
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or larger than the original volume.
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If the object is smaller, the snapshot volume could fill up as data is copied
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from the original to the snapshot, given sufficient activity on the original.
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In this situation, the snapshot is deactivated and additional
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I/O to the snapshot fails.
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</P
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><P
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>Base the size of the snapshot object on the amount of activity that
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is likely to take place on the original during the lifetime of the snapshot.
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The more changes that occur on the
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original and the longer the snapshot is expected to remain active,
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the larger the snapshot object should be.
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Clearly, determining this calculation is not simple and requires trial and
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error to determine the correct snapshot object size to use for a
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particular situation.
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The goal is to create a snapshot object large enough to prevent the
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shapshot from being
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deactivated if it fills up, yet small enough to not waste disk space.
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If the snapshot
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object is the same size as the original volume, or a little larger,
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to account for the snapshot mapping tables, the snapshot is
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never deactivated.
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</P
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><P
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>After you've created the snapshot object and saved the changes, the
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snapshot will be activated (as long as the snapshot child object is already active).
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This is a change from snapshots in EVMS 2.3.x and earlier, where the snapshot
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would not be activated until the object was made into an EVMS volume. If you
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wish to have an inactive snapshot, please add the name of the snapshot object
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to the "activate.exclude" line in the EVMS configuration file (see section about
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selective-activation for more details). If at any point you decide to deactivate a
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snapshot object while the original volume is still active, the snapshot will be reset.
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The next time that the snapshot object is activated, it will reflect the state of the
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original volume at that point in time, just as if the snapshot had just been created.</P
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><P
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>In order to mount the snapshot, the snapshot object must still be made into an
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EVMS volume. The name of this volume can be the same as or different than the
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name of the snapshot object.</P
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VALIGN="top"
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><A
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HREF="whatissnapshotting.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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VALIGN="top"
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>Home</A
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VALIGN="top"
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HREF="snapshotex.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>What is a snapshot?</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="evmscreatesnap.html"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Example: create a snapshot</TD
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></TR
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> |