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DATA PROTECTION TECHNOLOGIES FOR MICROSOFT PRIVATE CLOUD
Anupam ChakrabortyPrincipal Software [email protected]
Sunil YadavConsultant Software [email protected]
Soumen Acharya Senior Software [email protected]
Tushar Dethe Senior Software EngineerEMC [email protected]
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Table of Contents
Challenges in Protecting Private Cloud ...................................................................................... 3
What to backup for each virtual machine? .................................................................................. 5
Virtual Hard Disk .................................................................................................................... 5
Incremental backups & Synthetic full restore of Virtual Machines ............................................... 8
Synthetic full restore ..............................................................................................................10
Application consistency of Hyper-V host level backup ...............................................................11
Virtual Machine Backup .........................................................................................................11
Virtual Machine Restore ........................................................................................................13
Granular Level Restore (File Level Restore) ..........................................................................14
Hyper-V High Availability Virtual Machines on Cluster Shared Volumes ...................................14
Hype-V CSV Backup from a Single Node of a Cluster ...........................................................15
Using backup proxy for Hyper-V CSV configuration...............................................................17
Trouble Shooting Backup Failures ............................................................................................18
Partial Writer Backup .............................................................................................................18
Logs to check for backup failure ............................................................................................18
Microsoft Private Cloud Data Protection using Networker Module for Microsoft ........................20
Conclusion ................................................................................................................................21
Appendix ...................................................................................................................................23
Disclaimer: The views, processes or methodologies published in this article are those of the
authors. They do not necessarily reflect EMC Corporation’s views, processes or methodologies.
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Challenges in Protecting Private Cloud
Many organizations are building private cloud for better customization, utilization of resources,
control over data, and security. Though private cloud is inside an organization, it still satisfies
the characteristics of Cloud Computing – scalability and elasticity. Clouds are built with 3 main
resources namely, compute, storage, and network. For Microsoft, private cloud Hyper-V Servers
are mainly used for computation.
Scalability and high availability of Hyper-V Virtual Machines (VMs) are achieved by creating
Hyper-V Clusters on Cluster Shared Volume (CSV) or Scale-Out File Servers. But high
availability doesn’t eliminate the necessity of backup. As well, it doesn’t protect from deleting
data by mistake nor does it eliminate the need for regulatory compliance.
The scalability aspect of Hyper-V cluster has created challenges on existing backup
applications. The backup should complete in less time to meet the restore point objective (RPO)
even though the Hyper-V Cluster is scaled up from hundred to thousand machines. This article
describes the technology available to control your backup time in a scale-out environment.
Incremental backup is an aspect of data protection which is mandatory for accelerating your
backup speed, minimizing of network bandwidth, and reducing the backup window. Incremental
backup tracks the data changed since the last backup and sends the changed data over IP
network to the backup storage. In Hyper-V, incremental backup can be enabled for each virtual
machine via Hyper-V WMI API.
Incremental backups are good to reduce backup time but it increases restore time objective
(RTO). During restore, the Backup Administrator needs to restore a full backup and then needs
to apply a number of incremental backups to restore at the desired point in time. This process
can become time consuming. In this situation, how do we improve RTO? The RTO is improved
by synthesizing VMs in the backend. The synthesize process recreates a full VM from its
incremental backups and last full or synthetic-full backup. This article explains how the
synthesized backup can be created by merging differencing hard disk containing incremental
data to the parent hard disk.
In production environment, virtual machines (VMs) running application servers (SQL,
SharePoint, or Exchange) and Hypervisor server (Hyper-V Server: hosting those virtual
machines) may be loaded enough to handle the backup operation. A long running backup may
impact the performance of business critical applications. How do we improve backup
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performance in such situations? Can the backup operation be offloaded to a non-loaded
machine? Yes, it is possible. This article will describe the technology behind backup proxies.
This proxy node architecture is also scalable and multiple proxy nodes can be configured in a
cluster. These proxy nodes process VM backups in parallel when working to protect a large
scale environment in a short backup window. This architecture opens a new paradigm in data
protection to become an integral part of cloud backup and restores strategies.
The administrator has backed up the virtual machine. What is the guarantee that the backup is
consistent for the application running inside the virtual machines? This article describes how the
VSS writer inside the VMs takes part in the Volume Shadow Copy (VSS) snapshot process for
the virtual machines. This guarantees consistent backup for the application running inside virtual
machines. For example, an administrator can restore a SQL database or Exchange database
from the VM backup.
In a scalable environment, the number of VMs will keep growing. As the number of VMs grows,
if an error occurs during creation of snapshot of a single VM, the entire backup fails. The
snapshot of a virtual machine can fail for many reasons. For example, the VM hard disk is full or
VSS writer inside the VM has gone to a bad state. It is extremely difficult to troubleshoot the
problematic VMs and maintain the RPO for good VMs. This article describes how the partial
writer feature of Volume Shadow Copy Service helps to back up the healthy VMs and provides
diagnostic information for the bad VMs. Your Hyper-V Admins can use this information and fix
the issues themselves.
This article describes how EMC Networker® Module for Microsoft (NMM), a leading enterprise
backup and recovery software, solves the above problems. Configuration of backup for high
available cluster environments is a tedious process. Using NMM it is easy to configure backup
using a wizard that takes a few inputs from the user to validate the Hyper-V cluster environment
and configure backup. The cluster-aware backup of NMM protects your private cloud completely
and enables you to perform restore of a complete virtual machine application data inside the
VM. NetWorker integrated with Data Domain® (DD) ensures the optimal storage utilization.
Let us start with understanding the internals of VMs and what needs to be backed up to protect
a VM hosted in a Microsoft Private Cloud.
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What to back up for each virtual machine
In this section we will describe the components of a VM. Following are the components of each VM1:
Configuration XML
Chain of virtual hard disks
Saved State file
Memory .bin file
List of Snapshots, each of which contains:
Configuration XML
Saved State file
.avhd files
File type File extension Description
Virtual Hard Disk
files
.VHD (WS 2008 R2 &
earlier)
.VHDX (WS 2012 & later)
VMs created on Hyper-V uses the
Microsoft Virtual Hard Disk (VHDX)
specification to store virtual hard disks
for VMs. A VM can have one or more
virtual hard disks.
VM configuration .XML Hyper-V uses a VM configuration file in
XML format to store VM settings (for
example, CPU, memory, VHDs).
VM Running State
files
.BIN
.VSV
Hyper-V stores VM running state
(memory) files.
Virtual Hard Disk
Differencing files
.AVHD (WS 2008 R2 &
earlier)
.AVHDX (WS 2012 & later)
A VM snapshot creates one differencing
VHD file per VM VHD.
VM Configuration
Snapshot(s)
.XML A VM snapshot creates a copy of the
current VM configuration and saves it to
enable rollback.
Table 1: Components of a Virtual Machine (VM)
Virtual Hard Disk
In the previous section, we learned that Virtual Hard Disks (VHDs) are used as the hard disks
for virtual machines (VMs). A VHD is a large container file that simulates a hard disk image. We
will discuss different types of VHDs and particularly differencing VHD (AVHD) as they are
necessary for Hyper-V incremental backup and creating Synthetic full backups. There are three
types of Virtual Hard Disk files.
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1. Fixed Sized VHD - In fixed sized VHD, the space to store the file is allocated on the
physical storage when the virtual hard disk is created. For example, if you create a virtual
hard disk that is 2 GB in size, the system will create a host file approximately 2 GB in size.
2. Dynamically Expanding VHD - A dynamically expanding VHD at any given time is as large
as the actual data stored in it. Dynamically expanding VHDs are useful because they do not
require all the storage needed to contain the maximum size of the disk to be reserved up
front2. As more data is written, the file dynamically increases in size. For example, the size
of a file backing a virtual hard disk of 2 GB is initially around 2 megabytes (MB) on the host
file system. As data is written to this image, it grows to a maximum size of 2 GB.
3. Differencing VHD - A differencing disk is a virtual hard disk (VHD) that stores changes
made to another VHD or to the guest operating system. The differencing disk stores all
changes that would otherwise be made to the parent disk if the differencing disk was not
being used3.
A differencing VHD must be associated with a parent VHD. The parent VHD can be a fixed
sized, dynamically expanding or differencing VHD. In Hyper-V, differencing VHDs are also
created automatically whenever snapshots are taken of a virtual machine. A differencing hard
disk is merged with its parent hard disk when a user deletes a virtual machine snapshot.
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Figure 1: Parent-child relationships of differencing VHDs3
In Figure1, a Virtual Machine “W2K12” has a virtual hard disk “W2K12base.vhdx”. A snapshot of
the VM was taken before applying Service Pack 1. So a differencing VHD, “W2K12SP1.avhdx”
is created to store the changes made for installing Service Pack 1.
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Following are some PowerShell Cmdlets for performing various tasks with VHD:
PowerShell Cmdlets Description
New-VHD Creates one or more new virtual hard disks.
Get-VHD Gets the virtual hard disk object associated with a virtual hard
disk.
Set-VHD Sets the ParentPath or PhysicalSectorSizeBytes properties of a
virtual hard disk.
Mount-VHD Mounts one or more virtual hard disks.
Dismount-VHD Dismounts a virtual hard disk.
Convert-VHD Converts the format, version type, and block size of a virtual hard
disk file.
Optimize-VHD Optimizes the allocation of space used by virtual hard disk files,
except for fixed virtual hard disks.
Resize-VHD Resizes a virtual hard disk. This cmdlet lets you shrink or expand
the size of a virtual hard disk.
Merge-VHD Merges virtual hard disks. The Merge-VHD cmdlet merges virtual
hard disks in a differencing virtual hard disk chain. The merge is
from a specified source child disk to a specified destination child
disk. Merge is an offline operation; the virtual hard disk chain
must not be attached when merge is initiated.
Test-VHD Tests a virtual hard disk for any problems that would make it
unusable.
Table 2: PowerShell Cmdlets for performing various tasks with VHD12
We have described differencing VHD and merging a child VHD with its parent VHD in the above
section. These two concepts are used in Hyper-V incremental backup and creating synthetic full
backup from incremental backups.
Incremental backups and Synthetic full restore of Virtual Machines
Windows Server 2012 and later supports incremental backup of a virtual machine. To enable
incremental backup of a VM, Windows Server 2012 and later have introduced a new property,
‘IncrementalBackupEnabled’ of the ‘Msvm_VirtualSystemSettingData’ data type in WMI v2.
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Setting this property to ‘true’ enables incremental backup of the Virtual Machines. Hyper-V uses
a special type of checkpoints called recovery snapshots to track the differences between
backups4. Recovery snapshot is similar to regular virtual machine snapshot but they are
managed directly by Hyper-V Virtual Machine Manager.
To enable change tracking, the VM must be enabled for incremental backup using WMI API.
Full backup must be performed after incremental backup is first enabled. So the first full backup
copies complete VHD hierarchy, configuration XML, and leave a differential VHD around. The
next backup just backs up the differential virtual hard disk. Thus during each incremental
backup, only the differences (differencing virtual hard disk) is backed up. The virtual machines
configuration xml files which are very small in size are backed up every time. Thus, Hyper-V
incremental backup reduces backup time, network bandwidth, and disk space. This reduces the
backup window and helps to maintain RPO in a scaled out environment.
In Figure 2, during an incremental backup a VM will have two levels recovery snapshots. The
earlier recovery snapshot is merged into the base virtual hard disk at the end of the backup
process and one new recovery snapshot tracks the changes in the VM after the backup process
started5 . For example, Virtual Machine is enabled for incremental backup on Sunday. The first
backup on Sunday backs up the complete VHD hierarchy. Incremental backup of Monday and
Tuesday backs up only the differencing VHDs. The differencing VHDs backed up in each
incremental backup is merged with its previous backups to create Synthetic Full backup. On
Friday, restore from Synthetic Full backup of the VM was performed to get back the state of the
VM as it was in Tuesday.
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Figure 2: Incremental backup of a VM with 1 VHD and shows 3 days of backup (Sunday, Monday & Tuesday)
followed by Synthetic full restore on Friday5.
Synthetic full restore
Incremental backups are good to reduce backup time but it has a cost attached with it. During
restore, the Backup Administrator needs to restore a full backup and then needs to apply a
number of incremental backups to restore at the desired point in time. This increases restore
time objective (RTO) which can be controlled by synthesizing VM from incremental backups.
The differencing VHDs backed up during an incremental backup are merged with the VHDs
from previous backups to create a synthetic full backup of the virtual machine. The restore from
a synthetic-full VM reduces the time of restoring a chain of incremental backups during disaster
restore. Thus Synthetic full restore improves RTO.
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Application consistency of Hyper-V host level backup
Backup administrator often protects complete VM and installs backup application inside VM to
protect applications like SQL, Exchange, or SharePoint running inside the VM. This two-fold
data protection increases data traffic on Local Area Network (LAN), takes twice the amount of
backup storage, and consumes more CPU and I/O cycles from Hyper-V Server. In this section,
we have described why backup of a VM is sufficient and how it protects the applications running
inside the VM.
Volume Shadow Copy Service (VSS) facilitates backup operation for Windows OS. It co-
ordinates with backup Application (VSS Requestor), Applications to be backed up (Hyper-V \
SQL \ Exchange \ SharePoint, etc.) and storage to create application consistent shadow copies
for backup. Hyper-V VSS writer is used to create application-consistent backup of the VMs.
Suppose a SQL server is running inside your VM and you have copied the VM’s hard disk file
(VHD file) when the SQL Server was in the middle of a transaction. It is not guaranteed that the
SQL server will be in a consistent state after you restore the VM from the copied VHD. On the
other hand, if the backup is taken involving VSS framework, restore from this backup works.
This is because Hyper-V VSS writer allows SQL server to quiesce the data and put it in a point
in time before backup, such that restore from it works.
There are following cases where we recommend to backup applications inside the VM:
1) If a VM is configured with Pass-through disk or iSCSI disk that are not included in Hyper-
V back up, it is recommended to run backup application inside VM.
2) Backup agents inside VMs are capable to perform intelligent backups for clustered
application. For example, to back up only the passive copy of SQL Databases (SQL
DBs) on an Always-On Availability Group, administrator must configure backup inside
the VM.
Virtual Machine Backup
In Hyper-V host level backup, backup application talks to VSS and uses Hyper-V VSS writer on
the Hyper-V Server. Hyper-V VSS writer on Hyper-V Server talks to Hyper-V VSS integration
component (Hyper-V IC) inside the VM. Hyper-V IC inside the VM works like a backup
application and talks to VSS and VSS writer of the applications running inside the VM. The
following sequence diagram explains the mechanism of application consistent backup of VMs1.
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Figure 3: Hyper-V VSS Writer communicates with Hyper-V VSS IC (requestor) inside VMs to quiesce
application inside VMs for application consistent backup1
Figure 4: Sequence diagram for application consistent backup of VMs1
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The flow of calls to create a snapshot of a virtual machine:
1) To back up a VM, the backup application (VSS Requestor) calls into VSS to
DoSnapshotSet(). The backup application requests VSS to create consistent point-in-time of
the storage.
2) VSS call each of the registered writers and asked them to PrepareForSnapshot() including
the Hyper-V VSS writer.
3) Hyper-V VSS writers talks over its private channel to Virtual Machines Hyper-V VSS IC (that
is the guest requestor).
4) Hyper-V VSS IC also call the DoSnapshotSet() to the VSS framework inside the virtual
machine.
5) VSS call the PrepareForSnapshot() for all applications running inside the VM.
6) Applications quiesce themselves and returns control backup to VSS inside VM.
7) Inside VM the VSS takes snapshot using volsnap (system provider).
8) Control is returned to VSS which then notifies writer that VM quiesce is completed.
9) These steps are done for all the virtual machines selected for backup.
10) When VSS completes processing for all VMs, it create a snapshot on the physical machine.
VSS returns control to the backup App.
11) At this point, backup app copies the data from the snapshot created on the physical
machine.
Virtual Machine Restore
A virtual machine can be restored from the backup using VSS framework. Hyper-V VSS writer is
invoked with pre-restore call with metadata that includes a list of VMs going to be restored.
Hyper-V VSS writer looks at the metadata and checks if a VM already exists and deletes the
configuration XML and VHD files. Backup application then restores the files and fixes the
Access Control Lists (ACLs) to restore the files with right ACLs and then call post restore on
Hyper-V VSS writer. In post-restore step, Hyper-V VSS writer checks if all the files have
restored and then registers the Virtual Machines. If the VM has been restored to an alternate
location, for example, a different machine or different location on the same machine, it ensures
that all the paths are aligned, all the AVHDs are pointing to right parents, and fixes the network
configuration1.
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Granular Level Restore (File Level Restore)
In restore scenarios it is often required to retrieve a single file from the backup. In such
situations restoring an entire virtual machine is an overhead. Granular restore enables a user to
recover individual files or directories from the VM backup. A user can mount the backed up VHD
and then can explore the mount point from Windows Explorer. At this point, the user is actually
exploring data from backed up Virtual Hard Disk (VHD)4. You can drag and drop a file or folder
to another location. At that point, only the data you selected for copying is recovered. Thus, from
a VM backup a user can recover a complete VM or individual files within that VMs.
Hyper-V High Availability Virtual Machines on Cluster Shared Volumes
High Availability is one of the primary criteria for cloud infrastructure. Microsoft introduced
Cluster Shared Volumes (CSV) for Hyper-V High Availability Virtual Machines (VM). Microsoft
improved CSV for performance and backup\restore scenarios in Windows Server 2012 (WS
2012). In this section we will describe why CSV is essential for configuring High Available VMs
on Microsoft Private Cloud.
CSV is a clustered File System that provides simultaneous read-write access to all applications
running on all nodes of a cluster to a shared storage. Before introduction of CSV, an application
should have its own dedicated LUN and the LUN needs to failover with the application. With
CSV, the application can failover independent the LUN ownership.
Without CSV, a failover cluster only allows a given cluster disk (LUN) to be accessed by one
node at a time. Given this constraint, each Hyper-V virtual machine in the failover cluster
requires its own set of LUNs in order to be migrated or fail over independently of other virtual
machines. In this type of deployment, the number of LUNs increases with the addition of each
virtual machine, which makes management of LUNs and clustered virtual machines more
complex6.
In contrast, on a failover cluster that uses CSV, multiple virtual machines that are distributed
across multiple cluster nodes can all access their Virtual Hard Disk (VHD) files at the same time,
even if the VHD files are on a single disk (LUN) in the storage. The clustered virtual machines
can all fail over independently of one another6.
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Figure-5: Hyper-V CSV Configuration: VM1, VM2, VM3 are active on different nodes of a Hyper-V cluster and
their files (Config XML, VHD, snapshots) are present on the same CSV volume.
CSV provides a simultaneous read write access to the shared LUN from all cluster nodes.
Virtual machine can run on any node and still write to a volume mounted on one of the cluster
nodes (coordinator node). Metadata synchronization for the I/O is done on the CSV coordinator
node and metadata changes from all the cluster nodes for a particular CSV volume are routed
to the coordinator node. Metadata operations are very light weight operations. Metadata
changes occur in the scenarios like VM creation\deletion, VM power on\off, VM mobility (live
migration), snapshot creation, extending a dynamic VHD, and renaming a VHD. Metadata
updates are small operations that happen infrequently for VMs.
Hype-V CSV Backup from a Single Node of a Cluster
New architecture of CSV provides a backup infrastructure that delivers distributed application
consistent backup for cluster shared volume.
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Figure 6: Distributed application consistent backup of VMs in a cluster using new CSV writer and CSV
provider components7
CSV in WS 2012 and later supports distributed application consistent backup of VMs in a cluster
using new CSV writer and CSV provider components. In WS 2012, requestor can take a single
application consistent snapshot of all VMs running over multiple Hyper-V cluster nodes. VSS is
only initialized on the backup requesting node. Backup requesting node can be any node in the
cluster. VSS snapshots are created only on the backup requesting node7.
This arch diagram shows how the different components interact in WS 2012 to create an
application-consistent backup across a cluster. In this example, cluster has two nodes
“clusternode1” and “clusternode2”. VM1 and VM2 running on “clusternode1”; VM2 and VM3
running on “clusternode2”. All of them are running on same CSV volume. Backup is initiated by
a requestor from “clusternode1”. Backup requestor on clusternode1 talks to the VSS service to
gather the metadata and find out the files owned by VMs. In WS 2012, Hyper-V writer on the
local node reports all the VMs running on the local node. CSV writer on the local node serves
the metadata information of the VMs running on partner nodes using the Hyper-V writers
running on the partner nodes. For example, if we have a distributer 4-node cluster, from one
node we can talk to writers on the partner nodes and get the metadata of all VMs in the cluster7.
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CSV provider synchronizes the backup mechanism between local node and partner node. It co-
ordinates with Hyper-V VSS writer in partner node to quiesce and thaw the VMs running on the
partner nodes and making sure VMs are in consistent state to take backup. The Hyper-V VSS
writer on the local node quiesces and thaws the local VMs for backup. Thus, from one node the
backup application can take the backup of all VMs running on the cluster using CSV writer and
CSV provider7.
Using backup proxy for Hyper-V CSV configuration
We have seen in the previous section that in a Hyper-V CSV environment snapshot can be
created for all VMs in a CSV and backup can be taken from any node of the cluster. This
functionality of CSV has enabled backup proxy architecture. This proxy node architecture is also
scalable and multiple proxy nodes can be configured in a cluster to process VM backups in
parallel when working to protect a large scale environment in a short backup window. This
architecture opens a new paradigm in data protection. This becomes an integral part of cloud
backup and restores strategies.
Figure 7: Proxy backup architecture for high performance, impact free protection
VSS snapshot will always be created on the node which currently owns the cluster Physical
Disk resource associated with the CSV volume. If the backup is performed locally on the
coordinator node, the data access will be local and backup performance may be improved. This
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can be achieved by either initiating the backup application on the coordinator node or by moving
the Physical Disk resource locally to the node before initiating the backup. CSV ownership can
be moved seamlessly with no downtime. If you have maintenance window requirements that
require shortening the overall backup time, you may wish to optimize the performance of
backups when using software snapshots in one of the above ways8.
The other advantage of Proxy-based backup is that the CPU cost for backup is accounted on
the backup proxy; there is no extra CPU usage for the production server. There is no extra I/O
that production server needs to handle when the backup is going on. In Hyper-V proxy-based
backup, the production server is not impacted at all due to backup.
Troubleshooting Backup Failures
As the number of virtual machines grows it is extremely important to quickly troubleshoot the
cause of backup failure to maintain restore point objective (RPO). A whole backup can fail if an
error occurred during creation of snapshot of a single virtual machine. The snapshot of a virtual
machine can fails for many reasons. For instance, the hard disk inside the VM is full or VSS
writer inside VM goes to bad state. In this section, we will describe how to troubleshoot in case
of backup failure in your Microsoft private cloud environment.
Partial Writer Backup
Windows Server 2008 R2 Hyper-V VSS Writer and above provide support for partial backup
failure. Even if snapshot creation fails for some VMs, the backup can continue for other VMs.
Hyper-V VSS Writer reports the VMs which failed to back up. Suppose you are backing up 20
VMs and after successfully backup of 11 VMs the 12th VM fails to back up; the backup
application will continue backing up 13th VM onwards. The backup application will report 12th VM
failed to back up. In the following section we will see how to troubleshoot backup failure from
different logs.
Logs to check for backup failure
If Hyper-V backup fails, the backup administrator should check the Hyper-V VMMS log to figure
out which VM has failed. Hyper-V VMMS log is found at Event Viewer -> Applications and
Services Logs -> Microsoft -> Windows -> Hyper-V-VMMS->Admin. Hyper-V VMMS log also
states the reason of backup failure10. Following are two examples of troubleshooting backup
failure.
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In the first example, backup failed as the creation of shadow copy inside VM was unsuccessful.
When we logged inside the VM we found that there is no space in its system drive. The
administrator of the VM freed some space in the system drive and the next backup completed
successfully.
In the second example, backup failed for VM as a pass-through disk was attached to the VM.
We have discussed in section “Virtual Machine Backup” that snapshot can’t be taken for a pass-
through disk and in this case backup application should be installed inside the VM.
Figure 8: Backup of VM “TestVM1” failed as creation of Shadow copy inside the VM fails
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Figure 9: Backup of VM “PassThroughVM” failed as a pass-through disk was connected to it
Microsoft Private Cloud Data Protection using Networker Module for Microsoft
Figure 10: NetWorker Module for Microsoft (NMM) protecting a large Microsoft Private Cloud Deployment11
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EMC NetWorker backup and recovery software centralizes, automates, and accelerates data
backup and recovery. NetWorker delivers industry-leading performance and a wide range of
data protection options to safeguard critical business data.11
Following are Key features of the NetWorker Module for Microsoft in protecting MS private
cloud:
Centralized management
Protection for Hyper-V CSV and SMB 3.0 environments
Incremental backup and Synthetic full restore of VMs
Multi-Proxy backup for high performance, impact-free protection
Automated protection of newly created VMs
OS and application-consistent protection
No requirements for backup agents inside guest VM
Reporting VMs for which snapshot creation fails
New Virtualization Management via SCVMM
Microsoft Private Cloud protection offering disaster and granular file recoveries
Granular Level Recovery (GLR) for VM files recoveries in minutes
Integrated with Industry-leading data deduplication storage (Data Domain)
Tenant UI for FLR (web-based restore)
Conclusion
We have discussed the backup technologies available to reduce backup window in a scale out
Microsoft Private Cloud environment. A VM stores its hard disk in the Hyper-V Server using
VHD format. A special type of VHD, called differencing VHD, is associated with its parent VHD
and stores all changes made to the parent VHD. Hyper-V uses differencing VHD to track
changes between two backups. Incremental backup can be enabled for each VM using WMI
API. After the incremental backup is enabled, a differencing VHD tracks the changes from last
back. In each incremental backup the differencing VHD is only backed, accelerating backup
speed and optimizing network bandwidth. The differencing VHD is merged with the VHDs from
previous backups to create a synthetic-full VM in the backend. The restore from a synthetic-full
VM reduces the time of restoring a chain of incremental backups during disaster restore.
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We have seen that the Hyper-V VSS writer quiesces applications running inside VMs to take an
application-consistent backup of VMs. User can perform a complete VM restore, restore of an
application, and simply restore a file or directory from the VM backup.
Microsoft introduced Cluster Shared Volume which is a Cluster File System to support high
availability and scalability in cloud environments. Multiple virtual machines that are distributed
across multiple cluster nodes can all access their Virtual Hard Disk (VHD) files present on the
same CSV. In the new CSV architecture in Windows Server 2012 and later, snapshot of the
CSV volume can be created from any node in the cluster. This functionality of CSV has enabled
backup proxy architecture where a node in the Cluster is dedicated for backup operation. This
proxy node architecture is also scalable and multiple proxy nodes can be configured in a cluster
to process VM backups in parallel when working to protect a large scale environment in a short
backup window.
As the number of virtual machines grows it is extremely important to quickly troubleshoot the
cause of backup failure to maintain restore point objective (RPO). If snapshot creation fails for
some VMs, the Hyper-V VSS Writer reports those VMs and continues to backup other VMs.
Hyper-V VMMS log is found at Event Viewer -> Applications and Services Logs -> Microsoft ->
Windows -> Hyper-V-VMMS->Admin shows the reason of snapshot failure for VMs.
Finally, we discussed the features of NetWorker Module for Microsoft (NMM) that implements
the above technologies to protect Microsoft Private Cloud environments.
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Appendix
1. Hyper-V Backup Deep Dive: A Look under the Hood by Soumya Das Bhaumik.
http://channel9.msdn.com/Events/TechEd/NorthAmerica/2010/VIR322
2. Virtual Hard Disk (VHD) Architecture explained by Ranjana1.
http://blogs.technet.com/b/ranjanajain/archive/2010/03/23/virtual-hard-disk-vhd-
architecture-explained.aspx
3. Using differencing disks. http://technet.microsoft.com/en-
us/library/cc720381%28v=ws.10%29.aspx
4. Building a Backup Strategy for Your Private Cloud by Taylor Brown.
http://channel9.msdn.com/Events/TechEd/NorthAmerica/2014/DCIM-B319
5. Disaster Recovery in the Cloud with Hyper-V Backup and Replica by Andrew McMurray.
http://channel9.msdn.com/Series/Hybrid-Cloud-Workloads-High-Availability-and-
Disaster-Recovery/Mod2
6. Understanding Cluster Shared Volumes in a Failover Cluster:
http://technet.microsoft.com/en-us/library/dd759255.aspx
7. Cluster Shared Volumes Reborn in Windows Server 2012: Deep Dive by Amitabh
Tamhane & Vineeth Karinta.
http://channel9.msdn.com/Events/TechEd/NorthAmerica/2012/WSV430
8. Optimizing CSV Backup Performance by Elden Christensen.
http://blogs.msdn.com/b/clustering/archive/2013/05/06/10416507.aspx
9. Hyper-V over SMB: Remote File Storage Support in Windows Server 2012 Hyper-V by
Didier Van Hoye. http://technet.microsoft.com/en-in/video/hyper-v-over-smb-remote-file-
storage-support-in-windows-server-2012-hyper-v.aspx
10. Adventures with Hyper-V and Backup by Benjamin Armstrong.
http://blogs.msdn.com/b/virtual_pc_guy/archive/2010/02/22/adventures-with-hyper-v-
and-backup.aspx
11. Backup And Recovery For Microsoft-Based Private Clouds Leveraging The EMC Data
Protection Suite. https://www.emc.com/collateral/white-papers/h12654-backup-and-
recovery-for-microsoft-private-clouds-leveraging-dps-wp.pdf
12. Hyper-V Cmdlets in Windows PowerShell: https://technet.microsoft.com/en-
us/library/hh848559.aspx
2015 EMC Proven Professional Knowledge Sharing 24
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