DPM Issues I faced

1) Error: DPM does not have sufficient storage space available on the Recovery Point Volume to create new recovery  points. (ID 214)

When you get this error this means the recovery point volume may not have sufficient space for new recovery points or the attached disks may need to be refreshed from Computer Management console in DPM server. 

In my case DPM did not grow the volume automatically even though the option was selected.
Anyway, I grew the volume by 2 GB and issue resolved. I was able to run consistency check with success.

Volume Shadow Service

Windows Volume Shadow Service usually known as VSS runs as a service on Windows servers and clients.

VSS provides an interface among different components that need and create snapshots.

The components involved in snapshot creation:

1) VSS
2) Shadow requestor processes/applications (usually backup software)
3) Writer Processes
4) Shadow Providers

Shadow requestor application requests VSS that a shadow copy be created of the volume that has to be protected.

Shadow writer is a subsystem of software applications whose persistent data need to be backed-up, like, SQL server, Exchange server, etc.
The writers as soon as they receive a signal from VSS that a shadow copy needs to be created, they sync the data in memory to the disk and block all I/Os to the data to be backed-up essentially making data consistent for a brief period of time. Without this the backup data will be incomplete hence useless to apps like databases.

Shadow providers are the software or hardware that provide, i.e. create, the snapshots.
Once VSS confirms the I/O has been blocked by writers it communicates to the providers to create a shadow copy. A shadow copy can be created at the storage array side or in the OS itself.
Hardware providers ship drivers that can be installed on the OS for creating h/w shadow copies. These are created at the array side and whole LUN is copied.
Software providers employ their own way to create a copy of the volume on the OS itself.
System providers are shipped with Windows OS developed by Microsoft. These too create copy on the OS itself but are based on Copy-On-Write, i.e. they are differential copies and never full copy snapshots. (For more info on Full copy/COW snapshots, search for Snapshot technology online.)

To view shadow copies, use the command vssadmin.exe List Shadows, or vshadow.exe from VSSSDK.

Prerequisite Knowledge

To understand backup in Windows OS perspective you need to have working knowledge of:

1) Windows Volume Shadow Copy Service:

      Point-In-Time Copy service, Shadow copy is also known as "snapshot" or "Recovery Point" which is used in backup and recovery. For more info, visit http://technet.microsoft.com/en-us/library/cc785914.aspx

2) Microsoft Data Protection Manager:
     Data backup and recovery software from Microsoft (obviously!)

• The replicas are stored in the storage pool which consists of a set of disks on the DPM server, or on a custom volume
• protection begins with the creation of the replica of the data source
• The replica is synchronized, or updated, at regular intervals according to the settings that you configure
• The method that DPM uses to synchronize the replica depends on the type of data being protected
• If a replica is identified as being inconsistent, DPM performs a consistency check
• consistency check is a block-by-block verification of the replica against the data source
• The computer is protected when you install a DPM protection agent on the computer and add its data to a protection group
• Protection agents track changes to protected data and transfer the changes to the DPM server
• Protection groups are used to manage the protection of data sources on computers
• A protection group is a collection of data sources that share the same protection configuration
• The protection configuration is the collection of settings that are common to a protection group, such as the protection group name, protection policy, disk allocations, and replica creation method
• DPM stores a separate replica for each protection group member in the storage pool
• A replica is a complete point-in-time copy of the protected shares, folders, and files for a single volume on a protected computer
• A protection group member can be any of the following data sources:
  
  • A volume, share, or folder on a desktop computer, file server, or server cluster
  • A storage group on an Exchange server or server cluster
  • A database of an instance of SQL Server or server cluster
• A recovery point, also referred to as a snapshot, is a point-in-time copy of a replica stored on the Data Protection Manager (DPM) server

To start data protection, a full replica of the selected data must be copied to the allocated replica volume on the DPM server. Thereafter, the replica is periodically synchronized with changes to the protected data. DPM creates recovery points of each replica in a protection group according to a specified schedule. You can access the recovery points to recover previous versions of files in the event of data loss or corruption. You can recover data, and you can also configure end-user recovery so that users can recover their own data.

When you select recovery point times, DPM provides you with estimates for recovery range and maximum data loss. These estimates can help you specify a recovery point schedule that provides adequate data protection and meets your recovery goals. A maximum of eight recovery points can be scheduled per day.