Setup Guide

Best Practices 51
Using Storage Array Snapshots for LVM-Based
Storage Repositories
Using storage array snapshot features available on the Dell™ PowerVault™
MD3000, MD3000i and Dell EqualLogic
®
storage arrays, a point in time
copy of the Logical Volume Manager (LVM) based storage repositories can be
taken for tasks such as backup, data mining, reporting, testing software
upgrades, etc., in the virtual machines (VMs). A typical operation involves:
• Taking a snapshot of the storage repository (SR).
• Backing up the VM(s) metadata on an SR on the primary Citrix
XenServer
®
Dell™ Edition host.
• Attaching the snapshot to a secondary XenServer host.
• Restoring the VM(s) metadata on the secondary host.
A snapshot restore operation can also be performed to go back to a previous
known good state.
NOTE: XenServer 5.5 includes the ability to create snapshots at the VM level.
NOTE: A Xen VSS provider included as part of Citrix XenTools
®
enables quiesced
VM snapshots. Quiesced VM snapshots are only supported for Dell EqualLogic™
PS Series arrays and Dell EqualLogic storage repositories.
Quiesced snapshots take advantage of the Microsoft
®
Windows
®
Volume
Snapshot Service (VSS) for services that support it so that a supported application
(for example, Microsoft
Exchange
®
or Microsoft SQL Server
®
) can flush data to the
disk and prepare for the snapshot before it is taken.
For more information on creating and managing VM snapshots, see the XenServer
Reference Manual available on the Citrix XenServer Dell Edition website at
citrix.com/xenserver/dell.
With varying degree of impact on file system and application consistency and
service availability, you can run snapshot operations on an SR in essentially
three ways as discussed in the sections below.