Frequently asked questions on Microsoft Volume Shadow Copy Services (VSS) and NetBackup Snapshot Client

Article: 100021534
Last Published: 2013-10-24
Ratings: 1 0
Product(s): NetBackup

Problem

Frequently asked questions on Microsoft Volume Shadow Copy Services (VSS) and NetBackup Snapshot Client

Solution

Question 1:  While configuring a NetBackup SnapshotClient policy to use VSS as the snapshot method, what is the meaning of thoseprovider types?

    VSS-based snapshot methods offer ageneral interface to Windows Shadow Copy Services. VSS selects the actualsnapshot method depending on which snapshot provider is configured on theclient.  Although the provider selection is generally automatic, NetBackupSnapshot Client provides better control for the user by letting you decide theprovider especially when more than once provider can create the snapshot for theresource being backed up.

  Provider type 0: auto

      This is the default. If this is chosen, theVSS provider used will be decided in the following order: Hardware provider,Software Provider, System provider

  Provider type 1: System

      This is Microsoft's block level copy-on-writesnapshot provider built-in the operating system.  Not usable for offhostbackups.

  Provider type 2:Software

      This uses software based provider likeStorage Foundation for Windows (SFW) VSS provider. Useful when SFW installed onclient. If using an alternate host, it should have SFW installed well.

  Provider type 3: Hardware

       Uses the VSS provider from the arrayvendor on which the volume(s) reside.


Question 2:  Asprovider selection is automatic, why would I need to specifically choose aprovider type in the policy?

    There are situationswhere you would like to override the default selection logic of hardware,software, system order. Here are a few examples.

    2.1) Youprefer to make use of SFW or System provider  snapshots because thehardware provider  in your environment does not support a copy-on-writesnapshot that uses less space.
    2.2) It might be desirable tooverride hardware provider if all the volumes being backed up in the policy arenot from the same kind of array.
    2.3) When InstantRecovery is enabled in the policy, the provider type must be explicitly set.Else Instant Recovery based rollback operation cannot determine the correctprovider for restore operation.

Question 3:  When using VSS forsnapshots, does NetBackup Snapshot Client require free drive letters to mountthe snapshot for backups on source or offhost clients?

     No, VSS based snapshots are accessed duringbackups using snapshot volume GUID (hardware and system snapshots) or devicename (SFW snapshots). These snapshots are not exposed via drive letter or mountpoints. Hence there is no need to have free drive letters.

     Recently, (especially with Windows 2008) automountof snapshots had become a common practice. Veritas recommends disablingautomount as it is not needed when using Snapshot client. This can be done usingthe following methods.

     1. Use " mountvol/n"  from cmd OR
     2. Use diskpart utilityand set " automount disable"

Question 4:  I noticed inSnapshot Client compatibility matrix that hardware providers are certified forNTFS without volume manager. Does this mean that volume managers like SFW is notsupported with hardware providers in such configurations?

      Not necessarily. In VSS framework, theprovider code is developed and tested by provider vendor. Please check withhardware provider vendor (i.e. array vendor) if their provider is supported withdynamic disks and SFW. For the purpose of certifying a hardware VSS provider,Veritas tests it against the simplest configuration where no volume manager isin use. Veritas will work with you in case of issues with such configurationsif hardware vendor has certified dynamic disks. Microsoft states that dynamicdisks must be transported to another host as native support for dynamic diskscannot accommodate LUNs with duplicate signatures and configuration databasecontents.

Question 5: Is there a way to test my volumes in the policyusing VSS framework outside of NetBackup for troubleshooting purposes?

     Yes, you may use vshadow.exe utility fromMicrosoft. Please see article 323943 for a quick overview. For Windows 2008, diskshadow tool bundled with operating system can also be used. Moredetails are available from Microsoft documentation.





Was this content helpful?