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