Introduction

Many Microsoft Window applications (like Exchange, MS-SQL, etc) are critical to the daily core functionality for many companies and organizations. Managing the data backup for these applications presents new challenges for system administrators. While there is an ever increasing need for more and more data to be backed up, at the same time the system administrator must cope with the issue of shrinking backup windows in which the application can be taken offline in order to backup the application data. Another issue to contend with is the performance hit the production server takes when backup is running.
Microsoft Volume Shadow Copy Service (VSS) and SANRAD iSCSI V-Switch acting as VSS storage provider can help the system administrator resolve these issues by:
Eliminating the need to take the application offline.
Quickly responding to the increasing need for storage.
Enabling fast backup and restore by backing up to disks and offloading the backup performance hit from the production volumes and servers.

This application note describes VSS, how it works, the required basic configuration in order for VSS to work with the SANRAD V-Switch to create snapshots as well as the backup design options using VSS and SANRAD V-Switch. We use Veritas BackupExec (V10.0) to help us demonstrate taking backups with VSS using SANRAD V-Switch.
This application note assumes that the user has basic knowledge of how to use SANRAD V-Switch to configure volumes and expose them to the servers as disks. The user should also be familiar with Microsoft Iscsi initiator for connecting Windows 2003 server to the exposed iSCSI volumes by the SANRAD V-Switch.

What is VSS? Microsoft Volume Shadow Copy Service (VSS) provides the backup infrastructure for the Windows Server 2003 operating systems, as well as a mechanism for creating consistent point-in-time copies of data known as shadow copies or snapshots.
VSS can produce consistent snapshots by coordinating between different applications (business, file-system services, backup) and storage hardware.

The following steps describe VSS Architecture:
STEP 1. Path 1: The Requestor (usually a backup application) make a request to VSS (running on the application server) to create snapshots of production volumes so that backups can be made from the snapshots and not from the production volumes.
STEP 2. Path 2: If the volumes belong to an application that has a VSS Writer (VSS aware application like Exchange), the VSS requests the Writer to prepare the volumes. The Writer will usually flash the data to the disk and freeze IO writes from the application during the time the VSS takes the snapshots (usually few seconds). This ensures application data consistency when recovery is needed. If there is no VSS writer then VSS will go directly to the next step but there is no guarantee that the data is in a consistent state.
STEP 3. Path 3: VSS requests a provider to create a snapshot. There are three kinds of VSS providers: Hardware, Software and System. A system provider is part of the Windows 2003 OS and it will take snapshots and keep them but only at the OS level. A hardware provider is usually a storage provider, like SANRAD Iscsi V-Switch, which creates and maintains snapshots at the storage hardware level. VSS chooses the provider from a list (first on the list with priority given to hardware provider if one exists).
STEP 4. Path 4: VSS goes back to the VSS Writer (if it exists) and allows it to unfreeze the application I/O activity and resume normal activity.
STEP 5. Path 5: VSS goes back to the requestor (backup application) and gives it the location of the snapshots so it can start the backup from the snapshots.
STEP 6. Path 6: Once backup is complete, the requestor informs VSS which in turn informs the VSS provider to delete the snapshots.

Summary
The combined solution of Microsoft Volume Shadow Copy Service (VSS), SANRAD V-Switch as the VSS storage provider and backup VSS aware applications (like Veritas BackupExec V10) allow companies to offload backup jobs from the production environment, leave applications up for user access while backing up the data and have a data life cycle for regulations compliance.