| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="harddiskcontrollers">
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| 4 | <title>Hard Disk Controllers</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>
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| 8 | In a computing device, hard disks and CD/DVD drives are connected
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| 9 | to a device called a hard disk controller, which drives hard disk
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| 10 | operation and data transfers. <ph conkeyref="vbox-conkeyref-phrases/product-name"/> can emulate the most
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| 11 | common types of hard disk controllers typically found in computing
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| 12 | devices: IDE, SATA (AHCI), SCSI, SAS, USB-based, NVMe and
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| 13 | virtio-scsi mass storage devices.
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| 14 | </p>
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| 15 | <ul>
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| 16 | <li>
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| 17 | <p><b outputclass="bold">IDE (ATA)</b> controllers are a backward-compatible yet very
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| 18 | advanced extension of the disk controller in the IBM PC/AT (1984). Initially, this
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| 19 | interface worked only with hard disks, but was later extended to also support CD-ROM
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| 20 | drives and other types of removable media. In physical PCs, this standard uses flat ribbon
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| 21 | parallel cables with 40 or 80 wires. Each such cable can connect two devices, called
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| 22 | device 0 and device 1, to a controller. Typical PCs had two connectors for such cables. As
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| 23 | a result, support for up to four IDE devices was most common: primary device 0, primary
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| 24 | device 1, secondary device 0, and secondary device 1. </p>
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| 25 | <p>
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| 26 | In <ph conkeyref="vbox-conkeyref-phrases/product-name"/>, each virtual machine may have one IDE
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| 27 | controller enabled, which gives you up to four virtual storage
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| 28 | devices that you can attach to the machine. By default, one of
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| 29 | these virtual storage devices, device 0 on the secondary
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| 30 | channel, is preconfigured to be the virtual machine's virtual
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| 31 | CD/DVD drive. However, you can change the default setting.
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| 32 | </p>
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| 33 | <p>
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| 34 | Even if your guest OS has no support for SCSI or SATA devices,
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| 35 | it should always be able to see an IDE controller.
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| 36 | </p>
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| 37 | <p>
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| 38 | You can also select which exact type of IDE controller
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| 39 | hardware <ph conkeyref="vbox-conkeyref-phrases/product-name"/> should present to the virtual machine:
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| 40 | PIIX3, PIIX4, or ICH6. This makes no difference in terms of
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| 41 | performance, but if you import a virtual machine from another
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| 42 | virtualization product, the OS in that machine may expect a
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| 43 | particular controller type and crash if it is not found.
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| 44 | </p>
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| 45 | <p>
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| 46 | After you have created a new virtual machine with the
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| 47 | <b outputclass="bold">New Virtual Machine</b> wizard in
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| 48 | <ph conkeyref="vbox-conkeyref-phrases/vbox-mgr"/>, you will typically see one IDE controller in the
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| 49 | machine's <b outputclass="bold">Storage</b> settings.
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| 50 | The virtual CD/DVD drive will be attached to one of the four
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| 51 | ports of this controller.
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| 52 | </p>
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| 53 | </li>
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| 54 | <li>
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| 55 | <p><b outputclass="bold">Serial ATA (SATA)</b> is a more
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| 56 | recent standard than IDE. Compared to IDE, it supports both
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| 57 | much higher speeds and more devices per controller. Also, with
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| 58 | physical hardware, devices can be added and removed while the
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| 59 | system is running. The standard interface for SATA controllers
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| 60 | is called Advanced Host Controller Interface (AHCI).
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| 61 | </p>
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| 62 | <p>
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| 63 | Like a real SATA controller, <ph conkeyref="vbox-conkeyref-phrases/product-name"/>'s virtual SATA
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| 64 | controller operates faster and also consumes fewer CPU
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| 65 | resources than the virtual IDE controller. Also, this enables
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| 66 | you to connect up to 30 virtual hard disks to one machine
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| 67 | instead of just three, when compared to the <ph conkeyref="vbox-conkeyref-phrases/product-name"/> IDE
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| 68 | controller with a DVD drive attached.
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| 69 | </p>
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| 70 | <p>
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| 71 | For this reason, depending on the selected guest OS,
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| 72 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> uses SATA as the default for newly created
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| 73 | virtual machines. One virtual SATA controller is created by
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| 74 | default, and the default disk that is created with a new VM is
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| 75 | attached to this controller.
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| 76 | </p>
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| 77 | <note>
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| 78 | <p>
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| 79 | The entire SATA controller and the virtual disks attached to
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| 80 | it, including those in IDE compatibility mode, will not be
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| 81 | seen by OSes that do not have device support for AHCI. In
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| 82 | particular, <i>there is no support for AHCI in
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| 83 | Windows versions before Windows Vista</i>. Legacy
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| 84 | Windows versions such as Windows XP, even with SP3
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| 85 | installed, will not see such disks unless you install
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| 86 | additional drivers. It is possible to switch from IDE to
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| 87 | SATA after installation by installing the SATA drivers and
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| 88 | changing the controller type in the VM
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| 89 | <b outputclass="bold">Settings</b> window.
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| 90 | </p>
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| 91 | <p>
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| 92 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> recommends the Intel Matrix Storage drivers,
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| 93 | which can be downloaded from
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| 94 | <ph>http://downloadcenter.intel.com/Product_Filter.aspx?ProductID=2101</ph>.
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| 95 | </p>
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| 96 | </note>
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| 97 | <p>
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| 98 | To add a SATA controller to a machine for which it has not
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| 99 | been enabled by default, either because it was created by an
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| 100 | earlier version of <ph conkeyref="vbox-conkeyref-phrases/product-name"/>, or because SATA is not
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| 101 | supported by default by the selected guest OS, do the
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| 102 | following. Go to the <b outputclass="bold">Storage</b>
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| 103 | page of the machine's
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| 104 | <b outputclass="bold">Settings</b> window, click
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| 105 | <b outputclass="bold">Add Controller</b> under the
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| 106 | Storage Tree box and then select <b outputclass="bold">Add
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| 107 | SATA Controller</b>. The new controller appears as a
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| 108 | separate PCI device in the virtual machine, and you can add
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| 109 | virtual disks to it.
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| 110 | </p>
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| 111 | <p>
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| 112 | To change the IDE compatibility mode settings for the SATA controller, see <xref
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| 113 | href="vboxmanage-storagectl.dita"/>.
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| 114 | </p>
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| 115 | </li>
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| 116 | <li>
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| 117 | <p><b outputclass="bold">SCSI</b> is another established
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| 118 | industry standard, standing for Small Computer System
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| 119 | Interface. SCSI is as a generic interface for data transfer
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| 120 | between all kinds of devices, including storage devices. SCSI
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| 121 | is still used for connecting some hard disks and tape devices,
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| 122 | but it has mostly been displaced in commodity hardware. It is
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| 123 | still in common use in high-performance workstations and
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| 124 | servers.
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| 125 | </p>
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| 126 | <p>
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| 127 | Primarily for compatibility with other virtualization
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| 128 | software, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> optionally supports LSI Logic and
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| 129 | BusLogic SCSI controllers, to each of which up to fifteen
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| 130 | virtual hard disks can be attached.
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| 131 | </p>
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| 132 | <p>
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| 133 | To enable a SCSI controller, on the
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| 134 | <b outputclass="bold">Storage</b> page of a virtual
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| 135 | machine's <b outputclass="bold">Settings</b> window,
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| 136 | click <b outputclass="bold">Add Controller</b> under
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| 137 | the Storage Tree box and then select <b outputclass="bold">Add
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| 138 | SCSI Controller</b>. The new controller appears as a
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| 139 | separate PCI device in the virtual machine.
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| 140 | </p>
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| 141 | <note>
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| 142 | <p>
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| 143 | As with the other controller types, a SCSI controller will
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| 144 | only be seen by OSes with device support for it. Windows
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| 145 | 2003 and later ships with drivers for the LSI Logic
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| 146 | controller, while Windows NT 4.0 and Windows 2000 ships with
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| 147 | drivers for the BusLogic controller. Windows XP ships with
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| 148 | drivers for neither.
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| 149 | </p>
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| 150 | </note>
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| 151 | </li>
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| 152 | <li>
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| 153 | <p><b outputclass="bold">Serial Attached SCSI (SAS)</b> is
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| 154 | another bus standard which uses the SCSI command set. As
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| 155 | opposed to SCSI physical devices, serial cables are used
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| 156 | instead of parallel cables. This simplifies physical device
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| 157 | connections. In some ways, therefore, SAS is to SCSI what SATA
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| 158 | is to IDE: it enables more reliable and faster connections.
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| 159 | </p>
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| 160 | <p>
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| 161 | To support high-end guests which require SAS controllers,
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| 162 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> emulates a LSI Logic SAS controller, which can
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| 163 | be enabled much the same way as a SCSI controller. At this
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| 164 | time, up to 255 devices can be connected to the SAS
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| 165 | controller.
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| 166 | </p>
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| 167 | <note>
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| 168 | <p>
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| 169 | As with SATA, the SAS controller will only be seen by OSes
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| 170 | with device support for it. In particular, <i>there
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| 171 | is no support for SAS in Windows before Windows
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| 172 | Vista</i>. So Windows XP, even SP3, will not see such
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| 173 | disks unless you install additional drivers.
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| 174 | </p>
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| 175 | </note>
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| 176 | </li>
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| 177 | <li>
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| 178 | <p>
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| 179 | The <b outputclass="bold">USB mass storage device
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| 180 | class</b> is a standard to connect external storage
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| 181 | devices like hard disks or flash drives to a host through USB.
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| 182 | All major OSes support these devices and ship generic drivers
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| 183 | making third-party drivers superfluous. In particular, legacy
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| 184 | OSes without support for SATA controllers may benefit from USB
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| 185 | mass storage devices.
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| 186 | </p>
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| 187 | <p>
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| 188 | The virtual USB storage controller offered by <ph conkeyref="vbox-conkeyref-phrases/product-name"/>
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| 189 | works differently to the other storage controller types. While
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| 190 | most storage controllers appear as a single PCI device to the
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| 191 | guest with multiple disks attached to it, the USB-based
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| 192 | storage controller does not appear as virtual storage
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| 193 | controller. Each disk attached to the controller appears as a
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| 194 | dedicated USB device to the guest.
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| 195 | </p>
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| 196 | <note>
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| 197 | <p>
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| 198 | Booting from drives attached using USB is only supported
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| 199 | when EFI is used as the BIOS lacks USB support.
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| 200 | </p>
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| 201 | </note>
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| 202 | </li>
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| 203 | <li>
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| 204 | <p><b outputclass="bold">Non volatile memory express
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| 205 | (NVMe)</b> is a standard for connecting non volatile
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| 206 | memory (NVM) directly over PCI Express to lift the bandwidth
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| 207 | limitation of the previously used SATA protocol for
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| 208 | solid-state devices. Unlike other standards the command set is
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| 209 | very simple in order to achieve maximum throughput and is not
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| 210 | compatible with ATA or SCSI. OSes need to support NVMe devices
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| 211 | to make use of them. For example, Windows 8.1 added native
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| 212 | NVMe support. For Windows 7, native support was added with an
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| 213 | update.
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| 214 | </p>
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| 215 | <p>
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| 216 | The NVMe controller is part of the extension pack.
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| 217 | </p>
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| 218 | <note>
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| 219 | <p>
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| 220 | Booting from drives attached using NVMe is only supported
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| 221 | when EFI is used as the BIOS lacks the appropriate driver.
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| 222 | </p>
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| 223 | </note>
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| 224 | </li>
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| 225 | <li>
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| 226 | <p><b outputclass="bold">Virtual I/O Device SCSI</b> is a
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| 227 | standard to connect virtual storage devices like hard disks or
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| 228 | optical drives to a VM. Recent Linux and Windows versions
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| 229 | support these devices, but Windows needs additional drivers.
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| 230 | Currently virtio-scsi controller support is experimental.
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| 231 | </p>
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| 232 | <note>
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| 233 | <p>
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| 234 | The virtio-scsi controller will only be seen by OSes with
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| 235 | device support for it. In particular, <i>there is no
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| 236 | built-in support in Windows</i>. So Windows will not
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| 237 | see such disks unless you install additional drivers.
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| 238 | </p>
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| 239 | </note>
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| 240 | </li>
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| 241 | </ul>
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| 242 | <p>
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| 243 | In summary, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> gives you the following categories of
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| 244 | virtual storage slots:
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| 245 | </p>
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| 246 | <ul>
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| 247 | <li>
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| 248 | <p>
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| 249 | Four slots attached to the traditional IDE controller, which
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| 250 | are always present. One of these is typically a virtual CD/DVD
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| 251 | drive.
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| 252 | </p>
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| 253 | </li>
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| 254 | <li>
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| 255 | <p>
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| 256 | 30 slots attached to the SATA controller, if enabled and
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| 257 | supported by the guest OS.
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| 258 | </p>
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| 259 | </li>
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| 260 | <li>
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| 261 | <p>
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| 262 | 15 slots attached to the SCSI controller, if enabled and
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| 263 | supported by the guest OS.
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| 264 | </p>
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| 265 | </li>
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| 266 | <li>
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| 267 | <p>
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| 268 | Up to 255 slots attached to the SAS controller, if enabled and
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| 269 | supported by the guest OS.
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| 270 | </p>
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| 271 | </li>
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| 272 | <li>
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| 273 | <p>
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| 274 | Eight slots attached to the virtual USB controller, if enabled
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| 275 | and supported by the guest OS.
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| 276 | </p>
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| 277 | </li>
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| 278 | <li>
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| 279 | <p>
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| 280 | Up to 255 slots attached to the NVMe controller, if enabled
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| 281 | and supported by the guest OS.
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| 282 | </p>
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| 283 | </li>
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| 284 | <li>
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| 285 | <p>
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| 286 | Up to 256 slots attached to the virtio-scsi controller, if
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| 287 | enabled and supported by the guest OS.
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| 288 | </p>
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| 289 | </li>
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| 290 | </ul>
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| 291 | <p>
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| 292 | Given this large choice of storage controllers, you may not know
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| 293 | which one to choose. In general, you should avoid IDE unless it is
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| 294 | the only controller supported by your guest. Whether you use SATA,
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| 295 | SCSI, or SAS does not make any real difference. The variety of
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| 296 | controllers is only supplied by <ph conkeyref="vbox-conkeyref-phrases/product-name"/> for compatibility
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| 297 | with existing hardware and other hypervisors.
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| 298 | </p>
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| 299 | </body>
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| 300 |
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| 301 | </topic>
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