VirtualBox

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2010-12-2 下午12:12:12 (14 年 以前)
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Manual: guest additions updates

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  • trunk/doc/manual/en_US/user_GuestAdditions.xml

    r34539 r34599  
    1515    <title>Introduction</title>
    1616
    17     <para>As said in <xref linkend="virtintro" />, the Guest Additions are
    18     designed to be installed <emphasis>inside</emphasis> a virtual machine
     17    <para>As mentioned in <xref linkend="virtintro" />, the Guest Additions
     18    are designed to be installed <emphasis>inside</emphasis> a virtual machine
    1919    after the guest operating system has been installed. They consist of
    2020    device drivers and system applications that optimize the guest operating
    … …  
    4747
    4848        <glossentry>
     49          <glossterm>Shared folders</glossterm>
     50
     51          <glossdef>
     52            <para>These provide an easy way to exchange files between the host
     53            and the guest. Much like ordinary Windows network shares, you can
     54            tell VirtualBox to treat a certain host directory as a shared
     55            folder, and VirtualBox will make it available to the guest
     56            operating system as a network share, irrespective of whether guest
     57            actually has a network. For details, please refer to <xref
     58            linkend="sharedfolders" />.</para>
     59          </glossdef>
     60        </glossentry>
     61
     62        <glossentry>
    4963          <glossterm>Better video support</glossterm>
    5064
    … …  
    6478
    6579            <para>Finally, if the Guest Additions are installed, 3D graphics
    66             for guest applications can be accelerated; see <xref
    67             linkend="guestadd-3d" />.</para>
     80            and 2D video for guest applications can be accelerated; see <xref
     81            linkend="guestadd-video" />. </para>
     82          </glossdef>
     83        </glossentry>
     84
     85        <glossentry>
     86          <glossterm>Seamless windows</glossterm>
     87
     88          <glossdef>
     89            <para>With this feature, the individual windows that are displayed
     90            on the desktop of the virtual machine can be mapped on the host's
     91            desktop, as if the underlying application was actually running on
     92            the host. See <xref linkend="seamlesswindows" /> for
     93            details.</para>
     94          </glossdef>
     95        </glossentry>
     96
     97        <glossentry>
     98          <glossterm>Generic host/guest communication channels</glossterm>
     99
     100          <glossdef>
     101            <para>The Guest Additions enable you to control and monitor guest
     102            execution in ways other than those mentioned above. The so-called
     103            "guest properties" provide a generic string-based mechanism to
     104            exchange data bits between a guest and a host, some of which have
     105            special meanings for contolling and monitoring the guest; see
     106            <xref linkend="guestadd-guestprops" /> for details. </para>
     107
     108            <para>Additionally, applications can be started in a guest from
     109            the host; see <xref linkend="guestadd-guestcontrol" />. </para>
    68110          </glossdef>
    69111        </glossentry>
    … …  
    96138
    97139        <glossentry>
    98           <glossterm>Shared folders</glossterm>
    99 
    100           <glossdef>
    101             <para>These provide an easy way to exchange files between the host
    102             and the guest. Much like ordinary Windows network shares, you can
    103             tell VirtualBox to treat a certain host directory as a shared
    104             folder, and VirtualBox will make it available to the guest
    105             operating system as a network share. For details, please refer to
    106             <xref linkend="sharedfolders" />.</para>
    107           </glossdef>
    108         </glossentry>
    109 
    110         <glossentry>
    111           <glossterm>Seamless windows</glossterm>
    112 
    113           <glossdef>
    114             <para>With this feature, the individual windows that are displayed
    115             on the desktop of the virtual machine can be mapped on the host's
    116             desktop, as if the underlying application was actually running on
    117             the host. See <xref linkend="seamlesswindows" /> for
    118             details.</para>
    119           </glossdef>
    120         </glossentry>
    121 
    122         <glossentry>
    123140          <glossterm>Shared clipboard</glossterm>
    124141
    … …  
    953970    files of your host system from within the guest system. This is similar
    954971    how you would use network shares in Windows networks -- except that shared
    955     folders do not need require networking, so long as the Guest Additions are
    956     installed. Shared Folders are supported with Windows (2000 or newer),
    957     Linux and Solaris guests.</para>
     972    folders do not need require networking, only the Guest Additions. Shared
     973    Folders are supported with Windows (2000 or newer), Linux and Solaris
     974    guests.</para>
    958975
    959976    <para>Shared folders must physically reside on the
    960     <emphasis>host</emphasis> and are then shared with the guest; sharing is
    961     accomplished using a special service on the host and a file system driver
    962     for the guest, both of which are provided by VirtualBox. For Windows
    963     guests, shared folders are implemented as a pseudo-network redirector; for
    964     Linux and Solaris guests, the Guest Additions provide a virtual filesystem
    965     driver which handles communication with the host.</para>
     977    <emphasis>host</emphasis> and are then shared with the guest, which uses a
     978    special file system driver in the Guest Addition to talk to the host. For
     979    Windows guests, shared folders are implemented as a pseudo-network
     980    redirector; for Linux and Solaris guests, the Guest Additions provide a
     981    virtual file system.</para>
    966982
    967983    <para>To share a host folder with a virtual machine in VirtualBox, you
    … …  
    973989    particular virtual machine:<itemizedlist>
    974990        <listitem>
    975           <para>In the graphical user interface of a running virtual machine,
    976           you can select "Shared folders" from the "Devices" menu, or click on
    977           the folder icon on the status bar in the bottom right corner of the
    978           virtual machine window.</para>
    979         </listitem>
    980 
    981         <listitem>
    982           <para>If a virtual machine is not currently running, you can
    983           configure shared folders in each virtual machine's "Settings"
    984           dialog.</para>
    985         </listitem>
    986 
    987         <listitem>
    988           <para>From the command line, you can create shared folders using the
    989           VBoxManage command line interface; see <xref
    990           linkend="vboxmanage" />. The command is as follows: <screen>VBoxManage sharedfolder add "VM name" --name "sharename" --hostpath "C:\test"</screen></para>
     991          <para>In the window of a running VM, you can select "Shared folders"
     992          from the "Devices" menu, or click on the folder icon on the status
     993          bar in the bottom right corner.</para>
     994        </listitem>
     995
     996        <listitem>
     997          <para>If a VM is not currently running, you can configure shared
     998          folders in each virtual machine's "Settings" dialog.</para>
     999        </listitem>
     1000
     1001        <listitem>
     1002          <para>From the command line, you can create shared folders using
     1003          VBoxManage, as follows: <screen>VBoxManage sharedfolder add "VM name" --name "sharename" --hostpath "C:\test"</screen></para>
     1004
     1005          <para>See <xref linkend="vboxmanage-sharedfolder" /> for
     1006          details.</para>
    9911007        </listitem>
    9921008      </itemizedlist></para>
    … …  
    10221038      <para><itemizedlist>
    10231039          <listitem>
    1024             <para>In a Windows guest, starting with VirtualBox 1.5.0, shared
    1025             folders are browseable and are therefore visible in Windows
    1026             Explorer. So, to attach the host's shared folder to your Windows
    1027             guest, open Windows Explorer and look for it under "My Networking
    1028             Places" -&gt; "Entire Network" -&gt; "VirtualBox Shared Folders".
    1029             By right-clicking on a shared folder and selecting "Map network
    1030             drive" from the menu that pops up, you can assign a drive letter
    1031             to that shared folder.</para>
     1040            <para>In a Windows guest, shared folders are browseable and
     1041            therefore visible in Windows Explorer. So, to attach the host's
     1042            shared folder to your Windows guest, open Windows Explorer and
     1043            look for it under "My Networking Places" -&gt; "Entire Network"
     1044            -&gt; "VirtualBox Shared Folders". By right-clicking on a shared
     1045            folder and selecting "Map network drive" from the menu that pops
     1046            up, you can assign a drive letter to that shared folder.</para>
    10321047
    10331048            <para>Alternatively, on the Windows command line, use the
    … …  
    11091124      <title>Automatic mounting</title>
    11101125
    1111       <para>Starting with version 3.3.0, VirtualBox supports automatic
    1112       mounting support for shared folders. The installed Guest Additions will
    1113       then take care of all shared folders which are marked as being
    1114       auto-mounted as soon as a user is logged in to the guest OS. This makes
    1115       it more convenient instead of mounting shared folders manually described
    1116       in <xref linkend="sf_mount_manual" />.</para>
    1117 
    1118       <note>
    1119         <para>Auto-mounting currently is only supported on Windows, Linux and
    1120         Solaris guests.</para>
    1121       </note>
    1122 
    1123       <para>On Windows guests an auto-mounted shared folder will be
    1124       represented by an own drive letter (e.g.
    1125       <computeroutput>E:</computeroutput>), depending on the remaining free
    1126       drive letters of the system.</para>
    1127 
    1128       <para>On Linux and Solaris guests auto-mounted shared folders get
    1129       mounted into the <computeroutput>/media</computeroutput> directory,
    1130       along with the prefix <computeroutput>sf_</computeroutput>, so the
    1131       shared folder <computeroutput>myfiles</computeroutput> would be mounted
    1132       to <computeroutput>/media/sf_myfiles</computeroutput> on Linux and
    1133       <computeroutput>/mnt/sf_myfiles</computeroutput> on Solaris.</para>
    1134 
    1135       <para>To change the prefix <computeroutput>sf_</computeroutput> of a
    1136       given virtual machine, set the value of its
    1137       <computeroutput>/VirtualBox/GuestAdd/SharedFolders/MountPrefix</computeroutput>
    1138       guest property to another value; see <xref
    1139       linkend="guestadd-guestprops" /> for details.</para>
    1140 
    1141       <para>To get a user full access to the auto-mounted shared folders on
    1142       the guest this user needs to be part of the newly create group "vboxsf",
    1143       which is created by the VirtualBox Guest Additions installer. Without
    1144       being in that group read-only access is provided.</para>
    1145 
    1146       <para>To get changes applied, for example by adding new or deleting
    1147       auto-mounted shared folders while a VM is running, the guest OS needs to
    1148       be rebooted. However, this does not affect <xref
    1149       linkend="sf_mount_manual" />.</para>
     1126      <para>Starting with version 4.0, VirtualBox can mount shared folders
     1127      automatically, at your option. If automatic mounting is enabled for a
     1128      specific shared folder, the Guest Additions will automatically mount
     1129      that folder as soon as a user logs into the guest OS. The details depend
     1130      on the guest OS type:<itemizedlist>
     1131          <listitem>
     1132            <para>With Windows guests, any auto-mounted shared folder will
     1133            receive its own drive letter (e.g.
     1134            <computeroutput>E:</computeroutput>) depending on the free drive
     1135            letters remaining in the guest.</para>
     1136          </listitem>
     1137
     1138          <listitem>
     1139            <para>With Linux and Solaris guests, auto-mounted shared folders
     1140            are mounted into the <computeroutput>/media</computeroutput>
     1141            directory, along with the prefix
     1142            <computeroutput>sf_</computeroutput>. For example, the shared
     1143            folder <computeroutput>myfiles</computeroutput> would be mounted
     1144            to <computeroutput>/media/sf_myfiles</computeroutput> on Linux and
     1145            <computeroutput>/mnt/sf_myfiles</computeroutput> on
     1146            Solaris.</para>
     1147
     1148            <para>The guest property
     1149            <computeroutput>/VirtualBox/GuestAdd/SharedFolders/MountPrefix</computeroutput>
     1150            determines the prefix that is used. Change that guest property to
     1151            a value other than "sf" to change that prefix; see <xref
     1152            linkend="guestadd-guestprops" /> for details.<note>
     1153                <para>Read/write access to auto-mounted shared folders is only
     1154                granted to the user group
     1155                <computeroutput>vboxsf</computeroutput>, which is created by
     1156                the VirtualBox Guest Additions installer. You must therefore
     1157                add user accounts to that group for a user to have read/write
     1158                access. Other users are granted read-only access, even if the
     1159                shared folder in question has been defined as
     1160                read/write.</para>
     1161              </note></para>
     1162          </listitem>
     1163
     1164          <listitem>
     1165            <para>Solaris guests behave like Linux guests except that
     1166            <computeroutput>/mnt</computeroutput> is used for mounting the
     1167            shared folders instead of
     1168            <computeroutput>/media</computeroutput>.</para>
     1169          </listitem>
     1170        </itemizedlist></para>
     1171
     1172      <para>To have any changes to auto-mounted shared folders applied while a
     1173      VM is running, the guest OS needs to be rebooted. (This applies only to
     1174      auto-mounted shared folders, not the ones which are mounted
     1175      manually.)</para>
    11501176    </sect2>
    11511177  </sect1>
    11521178
    1153   <sect1 id="seamlesswindows">
    1154     <title>Seamless windows</title>
    1155 
    1156     <para>With the "seamless windows" feature of VirtualBox, you can have the
    1157     windows that are displayed within a virtual machine appear side by side
    1158     next to the windows of your host. This feature is supported for the
    1159     following guest operating systems (provided that the Guest Additions are
    1160     installed):<itemizedlist>
    1161         <listitem>
    1162           <para>Windows guests (support added with VirtualBox 1.5);</para>
    1163         </listitem>
    1164 
    1165         <listitem>
    1166           <para>Linux or Solaris/OpenSolaris guests with an X.org server
    1167           version 1.3 or higher<footnote>
    1168               <para>The X server version is not the same as the version of the
    1169               entire X.org suite. You can type <computeroutput>X
    1170               -version</computeroutput> in a terminal to find out about the
    1171               X.org server version level that is currently installed.</para>
    1172             </footnote> (support added with VirtualBox 1.6). The exception is
    1173           Fedora 9, due to a bug in its X server.</para>
    1174         </listitem>
    1175       </itemizedlist></para>
    1176 
    1177     <para>After seamless windows are enabled (see below), VirtualBox
    1178     suppresses the display of the Desktop background of your guest, allowing
    1179     you to run the windows of your guest operating system seamlessly next to
    1180     the windows of your host:</para>
    1181 
    1182     <para><mediaobject>
    1183         <imageobject>
    1184           <imagedata align="center" fileref="images/seamless.png" width="10cm" />
    1185         </imageobject>
    1186       </mediaobject>To enable seamless mode, after starting the virtual
    1187     machine, press the Host key (normally the right control key) together with
    1188     "L". This will enlarge the size of the VM's display to the size of your
    1189     host screen and mask out the guest operating system's background. To go
    1190     back to the "normal" VM display (i.e. to disable seamless windows), press
    1191     the Host key and "L" again.</para>
    1192   </sect1>
    1193 
    1194   <sect1>
     1179  <sect1 id="guestadd-video">
    11951180    <title>Hardware-accelerated graphics</title>
    11961181
    … …  
    13161301      to implement color space transformation and scaling</para>
    13171302    </sect2>
     1303  </sect1>
     1304
     1305  <sect1 id="seamlesswindows">
     1306    <title>Seamless windows</title>
     1307
     1308    <para>With the "seamless windows" feature of VirtualBox, you can have the
     1309    windows that are displayed within a virtual machine appear side by side
     1310    next to the windows of your host. This feature is supported for the
     1311    following guest operating systems (provided that the Guest Additions are
     1312    installed):<itemizedlist>
     1313        <listitem>
     1314          <para>Windows guests (support added with VirtualBox 1.5);</para>
     1315        </listitem>
     1316
     1317        <listitem>
     1318          <para>Linux or Solaris/OpenSolaris guests with an X.org server
     1319          version 1.3 or higher<footnote>
     1320              <para>The X server version is not the same as the version of the
     1321              entire X.org suite. You can type <computeroutput>X
     1322              -version</computeroutput> in a terminal to find out about the
     1323              X.org server version level that is currently installed.</para>
     1324            </footnote> (support added with VirtualBox 1.6). The exception is
     1325          Fedora 9, due to a bug in its X server.</para>
     1326        </listitem>
     1327      </itemizedlist></para>
     1328
     1329    <para>After seamless windows are enabled (see below), VirtualBox
     1330    suppresses the display of the Desktop background of your guest, allowing
     1331    you to run the windows of your guest operating system seamlessly next to
     1332    the windows of your host:</para>
     1333
     1334    <para><mediaobject>
     1335        <imageobject>
     1336          <imagedata align="center" fileref="images/seamless.png" width="10cm" />
     1337        </imageobject>
     1338      </mediaobject>To enable seamless mode, after starting the virtual
     1339    machine, press the Host key (normally the right control key) together with
     1340    "L". This will enlarge the size of the VM's display to the size of your
     1341    host screen and mask out the guest operating system's background. To go
     1342    back to the "normal" VM display (i.e. to disable seamless windows), press
     1343    the Host key and "L" again.</para>
    13181344  </sect1>
    13191345
    … …  
    14711497  </sect1>
    14721498
    1473   <sect1 id="guestadd-balloon">
    1474     <title>Memory ballooning</title>
    1475 
    1476     <para>Starting with version 3.2, the Guest Additions of VirtualBox can
    1477     change the amount of memory of a virtual machine while the machine is
    1478     running. Because of how this is implemented, this feature is called
    1479     "memory ballooning".</para>
    1480 
    1481     <para>Normally, to change the amount of memory allocated to a virtual
    1482     machine, one has to shut down the virtual machine entirely and change the
    1483     virtual machine's settings. With memory ballooning, memory that was
    1484     allocated for a virtual machine can be given to another virtual machine
    1485     without having to shut the machine down. This can be useful to temporarily
    1486     start another virtual machine, or in more complicated environments for
    1487     sophisticated memory management of many virtual machines that may be
    1488     running in parallel depending on how memory is used by the guests.</para>
    1489 
    1490     <para>When memory ballooning is requested, the VirtualBox Guest Additions
    1491     (which run inside the guest) allocate physical memory from the guest
    1492     operating system on the kernel level and lock this memory down in the
    1493     guest. This ensures that the guest will not use that memory any longer: no
    1494     guest applications can allocate it, and the guest operating system will
    1495     not use it either. VirtualBox can then re-use this memory and give it to a
    1496     second virtual machine.</para>
    1497 
    1498     <para>The memory made available through the ballooning mechanism is only
    1499     available for re-use by VirtualBox. It is <emphasis>not</emphasis>
    1500     returned as free memory to the host. Requesting balloon memory from a
    1501     running guest will therefore not increase the amount of free, unallocated
    1502     memory on the host.</para>
    1503 
    1504     <para>Effectively, memory ballooning is therefore a memory overcommitment
    1505     mechanism for multiple virtual machines while they are running.</para>
    1506 
    1507     <para>At this time, memory ballooning is only supported in VBoxManage, the
    1508     VirtualBox command-line utility. Use the following command to increase or
    1509     decrease the size of the memory balloon within a running virtual machine
    1510     that has Guest Additions installed: <screen>VBoxManage controlvm "VM name" guestmemoryballoon &lt;n&gt;</screen>
    1511     where <computeroutput>"VM name"</computeroutput> is the name or UUID of
    1512     the virtual machine in question and
    1513     <computeroutput>&lt;n&gt;</computeroutput> is the amount of memory to
    1514     allocate from the guest in megabytes; see <xref
    1515     linkend="vboxmanage-controlvm" /> for more information.</para>
    1516 
    1517     <para>You can also set a default balloon that will automatically be
    1518     requested from the VM every time after it has started up with the
    1519     following command: <screen>VBoxManage modifyvm "VM name" --guestmemoryballoon &lt;n&gt;</screen></para>
    1520 
    1521     <para>By default, no balloon memory is allocated. This is a VM setting,
    1522     like other <computeroutput>modifyvm</computeroutput> settings, and
    1523     therefore can only be set while the machine is shut down; see <xref
    1524     linkend="vboxmanage-modifyvm" />.</para>
    1525 
    1526     <para><note>
    1527         <para>VirtualBox supports memory ballooning only on 64-bit hosts,
    1528         memory ballooning is <emphasis>not</emphasis> supported on Mac OS X
    1529         hosts.</para>
    1530       </note></para>
    1531   </sect1>
    1532 
    1533   <sect1 id="guestadd-pagefusion">
    1534     <title>Page Fusion</title>
    1535 
    1536     <para>Page Fusion is a novel technique to further improve VM density on
    1537     the host, i.e. a way of overcommitting resources. It was first introduced
    1538     with VirtualBox 3.2 and is currently limited to VMs running Windows 2000
    1539     and later. In a typical scenario, dozens, up to hundreds of very similar
    1540     VMs are consolidated on a powerful host computer and the level of
    1541     consolidation is most often limited by the amount of RAM that can be
    1542     installed in a system at reasonable cost. Often, due to RAM exhaustion,
    1543     additional VMs cannot be started even though the host's CPUs still provide
    1544     capacity. To circumvent this restriction, hypervisors can benefit from the
    1545     fact that often, VMs are very similar (e.g. multiple VMs running Windows
    1546     XP Service Pack 2) and therefore contain a number of identical RAM cells.
    1547     The hypervisor can look for such duplicate data in memory, eliminate the
    1548     redundancy (deduplication) and thereby free additional memory.</para>
    1549 
    1550     <para>Traditional hypervisors use a technique often called "page sharing"
    1551     or "same page merging" where they go through all memory and compute
    1552     checksums (hashes) for each memory page. Then, they look for pages with
    1553     identical hashes and compare the content of the pages (if two pages
    1554     produce the same hash, it is very likely that the pages are identical in
    1555     content). Identical pages get eliminated so that all VMs point to the same
    1556     page as long as none of the VMs tries to modify the page. If such a page
    1557     gets modified, the previously eliminated duplicates get allocated again.
    1558     All this is fully transparent to the virtual machine. However, the
    1559     classical algorithm has several drawbacks. First of all, it takes rather
    1560     long to scan the complete memory (esp. when the system is not idling) so
    1561     the additional memory only becomes available after some time (this can be
    1562     hours or even days!). Also, the whole page sharing algorithm generally
    1563     consumes significant CPU resources and increases the virtualization
    1564     overhead by 10-20%.</para>
    1565 
    1566     <para>Page Fusion in VirtualBox uses the VirtualBox Guest Additions to
    1567     identify memory cells that are most likely identical across VMs and
    1568     therefore achieves most of the possible savings of page sharing almost
    1569     immediately and with almost no overhead. Page Fusion is also much less
    1570     likely to be tricked by identical memory that it will eliminate just to
    1571     learn seconds later that the memory will now change and having to perform
    1572     a highly expensive and often service disrupting reallocation.</para>
    1573 
    1574     <para>Page Fusion can be enabled for a VM using: <screen>VBoxManage modifyvm "VM name" --pagefusion on</screen></para>
    1575 
    1576     <para>You can observe Page Fusion operation using some metrics.
    1577     <computeroutput>RAM/VMM/Shared</computeroutput> shows the total amount of
    1578     fused pages whereas the per VM metric
    1579     <computeroutput>Guest/RAM/Usage/Shared</computeroutput> will return the
    1580     amount of fused memory for a given VM. Please refer to <xref
    1581     linkend="metrics" /> for information on how to query metrics.</para>
    1582 
    1583     <para><note>
    1584         <para>VirtualBox supports Page Fusion only on 64-bit host operating
    1585         systems. Mac OS X hosts are currently not supported. Page Fusion is
    1586         only available for Windows 2000 and later guests with current Guest
    1587         Additions.</para>
    1588       </note></para>
     1499  <sect1>
     1500    <title>Memory overcommitment</title>
     1501
     1502    <para>In server environments with many VMs; the Guest Additions can be
     1503    used to share physical host memory between several VMs, reducing the total
     1504    amount of memory in use by the VMs. If memory usage is the limiting factor
     1505    and CPU resources are still available, this can help with packing more VMs
     1506    on each host.</para>
     1507
     1508    <sect2 id="guestadd-balloon">
     1509      <title>Memory ballooning</title>
     1510
     1511      <para>Starting with version 3.2, the Guest Additions of VirtualBox can
     1512      change the amount of host memory that a VM uses while the machine is
     1513      running. Because of how this is implemented, this feature is called
     1514      "memory ballooning".</para>
     1515
     1516      <note>
     1517        <para>VirtualBox supports memory ballooning only on 64-bit hosts, and
     1518        it is not supported on Mac OS X hosts.</para>
     1519      </note>
     1520
     1521      <para>Normally, to change the amount of memory allocated to a virtual
     1522      machine, one has to shut down the virtual machine entirely and modify
     1523      its settings. With memory ballooning, memory that was allocated for a
     1524      virtual machine can be given to another virtual machine without having
     1525      to shut the machine down.</para>
     1526
     1527      <para>When memory ballooning is requested, the VirtualBox Guest
     1528      Additions (which run inside the guest) allocate physical memory from the
     1529      guest operating system on the kernel level and lock this memory down in
     1530      the guest. This ensures that the guest will not use that memory any
     1531      longer: no guest applications can allocate it, and the guest kernel will
     1532      not use it either. VirtualBox can then re-use this memory and give it to
     1533      another virtual machine.</para>
     1534
     1535      <para>The memory made available through the ballooning mechanism is only
     1536      available for re-use by VirtualBox. It is <emphasis>not</emphasis>
     1537      returned as free memory to the host. Requesting balloon memory from a
     1538      running guest will therefore not increase the amount of free,
     1539      unallocated memory on the host. Effectively, memory ballooning is
     1540      therefore a memory overcommitment mechanism for multiple virtual
     1541      machines while they are running. This can be useful to temporarily start
     1542      another machine, or in more complicated environments, for sophisticated
     1543      memory management of many virtual machines that may be running in
     1544      parallel depending on how memory is used by the guests.</para>
     1545
     1546      <para>At this time, memory ballooning is only supported through
     1547      VBoxManage. Use the following command to increase or decrease the size
     1548      of the memory balloon within a running virtual machine that has Guest
     1549      Additions installed: <screen>VBoxManage controlvm "VM name" guestmemoryballoon &lt;n&gt;</screen>where
     1550      <computeroutput>"VM name"</computeroutput> is the name or UUID of the
     1551      virtual machine in question and
     1552      <computeroutput>&lt;n&gt;</computeroutput> is the amount of memory to
     1553      allocate from the guest in megabytes. See <xref
     1554      linkend="vboxmanage-controlvm" /> for more information.</para>
     1555
     1556      <para>You can also set a default balloon that will automatically be
     1557      requested from the VM every time after it has started up with the
     1558      following command: <screen>VBoxManage modifyvm "VM name" --guestmemoryballoon &lt;n&gt;</screen></para>
     1559
     1560      <para>By default, no balloon memory is allocated. This is a VM setting,
     1561      like other <computeroutput>modifyvm</computeroutput> settings, and
     1562      therefore can only be set while the machine is shut down; see <xref
     1563      linkend="vboxmanage-modifyvm" />.</para>
     1564    </sect2>
     1565
     1566    <sect2 id="guestadd-pagefusion">
     1567      <title>Page Fusion</title>
     1568
     1569      <para>Whereas memory ballooning simply reduces the amount of RAM that is
     1570      available to a VM, Page Fusion works differently: it avoids memory
     1571      duplication between several similar running VMs.</para>
     1572
     1573      <para>In a server environment running several similar VMs (e.g. with
     1574      identical operating systems) on the same host, lots of memory pages are
     1575      identical. VirtualBox's Page Fusion technology, introduced with
     1576      VirtualBox 3.2, is a novel technique to efficiently identify these
     1577      identical memory pages and share them between multiple VMs.<note>
     1578          <para>VirtualBox supports Page Fusion only on 64-bit hosts, and it
     1579          is not supported on Mac OS X hosts. Page Fusion currently works only
     1580          with Windows guests (2000 and later).</para>
     1581        </note></para>
     1582
     1583      <para>The more similar the VMs on a given host are, the more efficiently
     1584      Page Fusion can reduce the amount of host memory that is in use. It
     1585      therefore works best if all VMs on a host run identical operating
     1586      systems (e.g. Windows XP Service Pack 2). Instead of having a complete
     1587      copy of each operating system in each VM, Page Fusion efficiently
     1588      identifies the identical memory pages in use by these operating systems
     1589      and eliminates the duplicates ("deduplication"), sharing host memory
     1590      between several machines.</para>
     1591
     1592      <para>If a VM tries to modify a page that is shared with other VMs, a
     1593      new page is allocated again for that VM with a copy of the shared page.
     1594      All this is fully transparent to the virtual machine.</para>
     1595
     1596      <para>You may be familiar with this kind of memory overcommitment from
     1597      other hypervisor products, which call this feature "page sharing" or
     1598      "same page merging". However, Page Fusion differs significantly from
     1599      those other solutions, whose approaches have several
     1600      drawbacks:<orderedlist>
     1601          <listitem>
     1602            <para>Traditional hypervisors scan <emphasis>all</emphasis> guest
     1603            memory and compute checksums (hashes) for every single memory
     1604            page. Then, they look for pages with identical hashes and compare
     1605            the entire content of those pages; if two pages produce the same
     1606            hash, it is very likely that the pages are identical in content.
     1607            This, of course, can take rather long, especially if the system is
     1608            not idling. As a result, the additional memory only becomes
     1609            available after a significant amount of time (this can be hours or
     1610            even days!). Even worse, this kind of page sharing algorithm
     1611            generally consumes significant CPU resources and increases the
     1612            virtualization overhead by 10-20%.</para>
     1613
     1614            <para>Page Fusion in VirtualBox uses logic in the VirtualBox Guest
     1615            Additions to quickly identify memory cells that are most likely
     1616            identical across VMs. It can therefore achieve most of the
     1617            possible savings of page sharing almost immediately and with
     1618            almost no overhead.</para>
     1619          </listitem>
     1620
     1621          <listitem>
     1622            <para>Page Fusion is also much less likely to be confused by
     1623            identical memory that it will eliminate just to learn seconds
     1624            later that the memory will now change and having to perform a
     1625            highly expensive and often service-disrupting reallocation.</para>
     1626          </listitem>
     1627        </orderedlist></para>
     1628
     1629      <para>At this time, Page Fusion can only be controlled with VBoxManage,
     1630      and only while a VM is shut down. To enable Page Fusion for a VM, use
     1631      the following command:<screen>VBoxManage modifyvm "VM name" --pagefusion on</screen></para>
     1632
     1633      <para>You can observe Page Fusion operation using some metrics.
     1634      <computeroutput>RAM/VMM/Shared</computeroutput> shows the total amount
     1635      of fused pages, whereas the per-VM metric
     1636      <computeroutput>Guest/RAM/Usage/Shared</computeroutput> will return the
     1637      amount of fused memory for a given VM. Please refer to <xref
     1638      linkend="metrics" /> for information on how to query metrics.</para>
     1639    </sect2>
    15891640  </sect1>
    15901641</chapter>

  • trunk/doc/manual/en_US/user_VBoxManage.xml

    r34563 r34599  
    18201820            destination medium. Only the portion of the source medium which
    18211821            fits into the destination medium is copied. This means if the
    1822             destination medium is smaller than the source only a part of it
    1823             is copied, and if the destination medium is larger than the source
     1822            destination medium is smaller than the source only a part of it is
     1823            copied, and if the destination medium is larger than the source
    18241824            the remaining part of the destination medium is unchanged.</para>
    18251825          </glossdef>
    … …  
    21232123  </sect1>
    21242124
    2125   <sect1>
     2125  <sect1 id="vboxmanage-sharedfolder">
    21262126    <title>VBoxManage sharedfolder add/remove</title>
    21272127
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