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iSCSI vs. FC for Meeting Mission Critical Requirements
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Using SANRAD V-Switch as the VSS hardware provider for Windows backups
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.
This article 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. It further discusses about Configuring Windows
Application server to use the V-Switch as the VSS Hardware Provider, Configuring the V-Switch
for VSS, Configuring the Backup Application to use VSS for the
backup job, Backup design options using the V-Switch as the VSS hardware provider, D2D - Offload the backup
from the production volumes, D2D - Offload the backup from
production servers, D2D - Save the backups in remote location
with SANRAD data replication, and D2D2T - Offload old backups
from disks to tape with SANRAD data replication. For further
reading click here
About the author:
None
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