A.4. Explanation of settings in the New Virtual Disk and Edit Virtual Disk windows Note The following tables do not include information on whether a power cycle is required because that information is not applicable to these scenarios. Table A.21. New Virtual Disk and Edit Virtual Disk settings: Image Field Name Description Size(GB) The size of the new virtual disk in GB. Alias The name of the virtual disk, limited to 40 characters. Description A description of the virtual disk. This field is recommended but not mandatory. Interface The virtual interface the disk presents to virtual machines. VirtIO is faster, but requires drivers. Red Hat Enterprise Linux 5 and later include these drivers. Windows does not include these drivers, but you can install them from the virtio-win ISO image. IDE and SATA devices do not require special drivers. The interface type can be updated after stopping all virtual machines that the disk is attached to. Data Center The data center in which the virtual disk will be available. Storage Domain The storage domain in which the virtual disk will be stored. The drop-down list shows all storage domains available in the given data center, and also shows the total space and currently available space in the storage domain. Allocation Policy The provisioning policy for the new virtual disk. Preallocated allocates the entire size of the disk on the storage domain at the time the virtual disk is created. The virtual size and the actual size of a preallocated disk are the same. Preallocated virtual disks take more time to create than thin provisioned virtual disks, but have better read and write performance. Preallocated virtual disks are recommended for servers and other I/O intensive virtual machines. If a virtual machine is able to write more than 1 GB every four seconds, use preallocated disks where possible. Thin Provision allocates 1 GB at the time the virtual disk is created and sets a maximum limit on the size to which the disk can grow. The virtual size of the disk is the maximum limit; the actual size of the disk is the space that has been allocated so far. Thin provisioned disks are faster to create than preallocated disks and allow for storage over-commitment. Thin provisioned virtual disks are recommended for desktops. Disk Profile The disk profile assigned to the virtual disk. Disk profiles define the maximum amount of throughput and the maximum level of input and output operations for a virtual disk in a storage domain. Disk profiles are defined on the storage domain level based on storage quality of service entries created for data centers. Activate Disk(s) Activate the virtual disk immediately after creation. This option is not available when creating a floating disk. Wipe After Delete Allows you to enable enhanced security for deletion of sensitive material when the virtual disk is deleted. Bootable Enables the bootable flag on the virtual disk. Shareable Attaches the virtual disk to more than one virtual machine at a time. Read Only Allows you to set the disk as read-only. The same disk can be attached as read-only to one virtual machine, and as rewritable to another. This option is not available when creating a floating disk. Enable Discard Allows you to shrink a thin provisioned disk while the virtual machine is up. For block storage, the underlying storage device must support discard calls, and the option cannot be used with Wipe After Delete unless the underlying storage supports the discard_zeroes_data property. For file storage, the underlying file system and the block device must support discard calls. If all requirements are met, SCSI UNMAP commands issued from guest virtual machines is passed on by QEMU to the underlying storage to free up the unused space. The Direct LUN settings can be displayed in either Targets > LUNs or LUNs > Targets . Targets > LUNs sorts available LUNs according to the host on which they are discovered, whereas LUNs > Targets displays a single list of LUNs. Table A.22. New Virtual Disk and Edit Virtual Disk settings: Direct LUN Field Name Description Alias The name of the virtual disk, limited to 40 characters. Description A description of the virtual disk. This field is recommended but not mandatory. By default the last 4 characters of the LUN ID is inserted into the field. The default behavior can be configured by setting the PopulateDirectLUNDiskDescriptionWithLUNId configuration key to the appropriate value using the engine-config command. The configuration key can be set to -1 for the full LUN ID to be used, or 0 for this feature to be ignored. A positive integer populates the description with the corresponding number of characters of the LUN ID. Interface The virtual interface the disk presents to virtual machines. VirtIO is faster, but requires drivers. Red Hat Enterprise Linux 5 and later include these drivers. Windows does not include these drivers, but you can install them from the virtio-win ISO image. IDE and SATA devices do not require special drivers. The interface type can be updated after stopping all virtual machines that the disk is attached to. Data Center The data center in which the virtual disk will be available. Host The host on which the LUN will be mounted. You can select any host in the data center. Storage Type The type of external LUN to add. You can select from either iSCSI or Fibre Channel . Discover Targets This section can be expanded when you are using iSCSI external LUNs and Targets > LUNs is selected. Address - The host name or IP address of the target server. Port - The port by which to attempt a connection to the target server. The default port is 3260. User Authentication - The iSCSI server requires User Authentication. The User Authentication field is visible when you are using iSCSI external LUNs. CHAP user name - The user name of a user with permission to log in to LUNs. This field is accessible when the User Authentication check box is selected. CHAP password - The password of a user with permission to log in to LUNs. This field is accessible when the User Authentication check box is selected. Activate Disk(s) Activate the virtual disk immediately after creation. This option is not available when creating a floating disk. Bootable Allows you to enable the bootable flag on the virtual disk. Shareable Allows you to attach the virtual disk to more than one virtual machine at a time. Read Only Allows you to set the disk as read-only. The same disk can be attached as read-only to one virtual machine, and as rewritable to another. This option is not available when creating a floating disk. Enable Discard Allows you to shrink a thin provisioned disk while the virtual machine is up. With this option enabled, SCSI UNMAP commands issued from guest virtual machines is passed on by QEMU to the underlying storage to free up the unused space. Enable SCSI Pass-Through Available when the Interface is set to VirtIO-SCSI . Selecting this check box enables passthrough of a physical SCSI device to the virtual disk. A VirtIO-SCSI interface with SCSI passthrough enabled automatically includes SCSI discard support. Read Only is not supported when this check box is selected. When this check box is not selected, the virtual disk uses an emulated SCSI device. Read Only is supported on emulated VirtIO-SCSI disks. Allow Privileged SCSI I/O Available when the Enable SCSI Pass-Through check box is selected. Selecting this check box enables unfiltered SCSI Generic I/O (SG_IO) access, allowing privileged SG_IO commands on the disk. This is required for persistent reservations. Using SCSI Reservation Available when the Enable SCSI Pass-Through and Allow Privileged SCSI I/O check boxes are selected. Selecting this check box disables migration for any virtual machine using this disk, to prevent virtual machines that are using SCSI reservation from losing access to the disk. Fill in the fields in the Discover Targets section and click Discover to discover the target server. You can then click the Login All button to list the available LUNs on the target server and, using the radio buttons to each LUN, select the LUN to add. Using LUNs directly as virtual machine hard disk images removes a layer of abstraction between your virtual machines and their data. The following considerations must be made when using a direct LUN as a virtual machine hard disk image: Live storage migration of direct LUN hard disk images is not supported. Direct LUN disks are not included in virtual machine exports. Direct LUN disks are not included in virtual machine snapshots. Important Mounting a journaled file system requires read-write access. Using the Read Only option is not appropriate for virtual disks that contain such file systems (e.g. EXT3 , EXT4 , or XFS ).

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