HPP Enterprises P4000 SAN - Manual (Page 6)

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Performance, capacity and availability can be scaled on-demand and on-line.
Storage repository
A storage repository (SR) is defined as a container of storage to which XenServer Virtual Machine
data will be stored. Although SRs can support locally connected storage types such as IDE, SATA,
SCSI and SAS drives, remotely connected iSCSI SAN storage will be discussed in this document.
Storage Repositories abstract the underlying differences in the storage connectivity, although
differences between local and remotely connected storage repositories enable specific XenServer
Resource Pool capabilities such as High Availability and XenMotion. The demands of a XenServer
resource pool dictate that storage must be equally accessible amongst all hosts and therefore data
must not be stored on local SRs
Virtual disk image
A virtual disk image (VDI) is the disk presented to the Virtual Machine and its OS as a local disk (even
if the disk image is stored remotely). This image will be stored in the container of a SR. Although
multiple VDIs may be stored on a single SR, it is considered best practice to store one VDI per SR. It is
also considered best practice to have one Virtual Machine allocated to a single VDI. VDIs can be
stored in different formats depending upon the type of connectivity afforded to Storage Repository.
Physical block device
A physical block device (PBD) is a connector that describes how XenServer hosts find and connect to
an SR.
Virtual block device
A virtual block device (VBD) is a connector that describes how a VM connects to its associated VDI,
which is located on a SR.
Overview of XenServer iSCSI storage repositories
XenServer hosts access HP StorageWorks P4000 iSCSI storage repositories (SRs) either using the
open-iSCSI software initiator or thru an iSCSI Host Bus Adapter (HBA). XenServer SRs regardless of
the access method, use Linux Logical Volume Manager (LVM) as the underlying file system to store
Virtual Disk Images (VDI). Although multiple virtual disks may reside on a single storage repository, it
is recommended that a single VDI occupy the space of an SR for optimum performance.
iSCSI using the software initiator (lvmoiscsi)
In this method, the open-iSCSI software initiator is used to connect to an iSCSI volume over the
Ethernet network. The iSCSI volume is presented to a XenServer or Resource Pool thru this connection.
iSCSI Host Bus Adapter (HBA) (lvmohba)
In this method, a specialized hardware interface, an iSCSI Host Bus Adapter, is used to connect to an
iSCSI volume over the Ethernet network. The iSCSI volume is presented to a XenServer or Resource
Pool through this connection.
lvmoiscsi is the method used in this paper. Please refer to the XenServer Administrator’s Guide for
configuration requirements of lvmohba.
SAN connectivity
Physically connected via an Ethernet IP infrastructure, HP StorageWorks P4000 SANs provide storage
for XenServer hosts using the iSCSI block-based storage protocol to carry storage data from host to