XenServer Administrator's Guide 4.1.0

Storage

• The LVM format can be used on either local disk or shared storage. Shared LVM access can be provided

using either an iSCSI or a Fibre Channel LUN hosted on a network filer that allows shared access by

multiple initiators or HBAs.

• Managed Netapp LUNs are accessible via the Netapp SR driver type, and are hosted on a Network

Appliance device running a version of Ontap 7.0 or greater. LUNs are allocated and mapped dynamically

to the host via the XenServer Host management framework.

3.1.3. Managing Storage

In working with the XenServer Host CLI, there are four object classes that are used to describe, configure,

and manage storage:

• Storage Repositories (SRs) are storage targets containing homogeneous virtual disks (VDIs). SR com-

mands provide operations for creating, destroying, resizing, cloning, connecting and discovering the in-

dividual Virtual Disk Images (VDIs) that they contain.

A storage repository is a persistent, on-disk data structure. So the act of "creating" a new SR is similar

to that of formatting a disk -- for most SR types, creating a new SR involves erasing any existing data

on the specified storage target. The exception is NFS SRs, which create a new directory on the filer

leaving existing NFS SRs as they were. SRs are long-lived, and may in some cases be shared among

XenServer Hosts, or moved between them. CLI operations to manage storage repositories are described

in Section 5.4.13, “SR commands”.

• Physical Block Devices (PBDs) represent the interface between a physical server and an attached SR.

PBDs are connector objects that allow a given SR to be mapped to a XenServer Host. PBDs store the

device configuration fields that are used to connect to and interact with a given storage target. For ex-

ample, NFS device configuration includes the IP address of the NFS server and the associated path

that the XenServer Host mounts. PBD objects manage the run-time attachment of a given SR to a given

XenServer Host. CLI operations relating to PBDs are described in Section 5.4.9, “PBD commands”.

• Virtual Disk Images (VDIs) are an on-disk representation of a virtual disk provided to a VM. VDIs are the

fundamental unit of virtualized storage in XenServer.

Similar to SRs, VDIs are persistent, on-disk objects that exist independently of XenServer Hosts. CLI

operations to manage VDIs are presented in Section 5.4.19, “VDI commands”.

• Virtual Block Devices (VBDs) are a connector object (similar to the PBD described above) that allows

mappings between VDIs and Virtual Machines (VMs). In addition to providing a mechanism to attach (or

plug) a VDI into a VM, VBDs allow the fine-tuning of parameters regarding QoS (quality of service), statis-

tics, and the bootability of a given VDI. CLI operations relating to VBDs are described in Section 5.4.18,

“VBD commands”.

3.2. Storage Repository Types

This section provides descriptions of the physical storage types that XenServer supports. Device configu-

ration options and examples of creating SRs are given for each type.

SR type Description Shared? Sparse? VDI Resize? Fast Clone?

ext VHD on Local Disk no yes no yes

nfs VHD on Network File System yes yes no yes

lvm Logical Volume Management on

Local Disk

no no yes no