mirror of https://github.com/tLDP/LDP
142 lines
4.9 KiB
XML
142 lines
4.9 KiB
XML
<appendix id="appxdrivelink"><title>The drive link plug-in</title>
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<para>The EVMS drive link plug-in is an aggregating plug-in that
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combines storage objects into a single object.
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The resulting drive link storage object can be made into a
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compatibility volume, EVMS volume, or even be consumed by
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higher-level storage objects.
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The drive link plug-in is one way to create large storage objects and
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volumes from smaller individual pieces.
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</para>
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<sect1 id="how"><title>How drive linking is implemented</title>
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<para>The drive link plug-in consumes storage objects, called link
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objects, producing a larger drive link object whose address space spans
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the link objects.
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The drive link plug-in knows how to assemble the link objects so as to
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create the exact same address space every time.
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The information required to do this is kept on each link child as persistent
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drive-link metadata.
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During discovery, the drive link plug-in inspects each known storage
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object for this metadata.
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The presence of this metadata identifies the storage object as a link object.
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The information contained in the metadata is sufficient to:</para>
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<itemizedlist>
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<listitem>
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<para>Identify the link object itself.</para>
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</listitem>
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<listitem>
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<para>Identify the drive link storage object that the link object belongs to.
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</para>
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</listitem>
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<listitem>
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<para>Identify all link objects belonging to the drive link storage.
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object</para>
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</listitem>
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<listitem>
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<para>Establish the order in which to combine the child link objects.</para>
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</listitem>
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</itemizedlist>
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<para>If any link objects are missing at the conclusion of the discovery
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process, the drive link storage object contains gaps where the missing
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link objects occur.
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In such cases, the drive link plug-in attempts to fill in the gap with a
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substitute link object and construct the drive link storage object in
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read-only mode, which allows for recovery action.
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The missing object might reside on removable storage that has been removed or
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perhaps a lower layer plug-in failed to produce the missing object.
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Whatever the reason, a read-only drive link storage object, together
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logging errors, help you take the appropriate actions to recover the drive link.
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</para>
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</sect1>
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<sect1 id="createlink"><title>Creating a drive link</title>
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<para>
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The drive link plug-in provides a list of acceptable objects from which it can create a drive link object.
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When you create an EVMS storage object and choose
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the drive link plug-in, a list of acceptable objects is provided that you
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simply choose from.
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The ordering of the drive link is implied by the order in which you pick objects from the
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provided list.
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After you provide a name for the drive link, the identified link
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objects are consumed and the new drive link object is produced.
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There are no create options.
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</para>
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</sect1>
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<sect1 id="dlexpandpart"><title>Expanding partitions</title>
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<para>
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Drive links are aggregating objects that can be expanded in the following ways:</para>
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<itemizedlist>
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<listitem>
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<para>
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By adding an additional storage object to the end of the drive link.
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</para>
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</listitem>
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<listitem>
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<para>
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By expanding the last storage object in the drive link.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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If the expansion point is the drive link storage object, you can perform the
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expansion by choosing from a list of objects that the drive link plug-in
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finds acceptable for the expansion.
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Multiple objects can be selected and added to the drive link.
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</para>
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<para>
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If the expansion point is a link object, then the
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plug-in that produced the link object does the expansion.
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For example, if the link object was a segment, then the segment manager
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plug-in that produced the storage object expands the link object.
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Afterward, the drive link storage object is resized to reflect the expansion.
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</para>
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<para>
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There are no expand options.
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</para>
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</sect1>
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<sect1 id="dlshrink"><title>Shrinking a drive link</title>
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<para>
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Drive links can be shrunk in the following ways:
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<itemizedlist>
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<listitem><para>By removing link objects from the end of the drive link.</para>
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</listitem>
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<listitem><para>By shrinking the last storage object in the drive link.</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>Removing
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a link object from anywhere other than the end of the drive link produces a gap in the drive link address
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space, similar to the gap produced by missing link objects.
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The drive link plug-in attempts to orchestrate the shrinking of a
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drive-link storage object by only listing the last link object.
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If you select this object, the drive link plug-in then lists the next-to-last link object, and so forth, moving backward through the link
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objects to satisfy the shrink command.
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</para>
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<para>
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There are no shrink options.
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</para>
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</sect1>
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<sect1 id="dldelete"><title>Deleting a drive link</title>
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<para>
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A drive link can be deleted as long as it is not currently a
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compatibility volume, an EVMS volume, or consumed by another EVMS plug-in.
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</para>
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<para>
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No options are available for deleting a drive link storage object.
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</para>
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</sect1>
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</appendix>
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