Oracle restore question

Last post 12-18-2018, 3:44 PM by efg. 11 replies.
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  • Oracle restore question
    Posted: 11-05-2018, 11:08 AM

    Hi All.

    Please help me clarifying.

    If I do a Oracle backup with 4 Data Backup streams and afterwards do a restore with 8 streams, will the restore actually run with 8 streams or are Commvault "giving" Oracle/RMAN 8 streams but actually only use the 4 streams for the restore?

     

    Found this statemen in an old post from 2015:

    "One note...  RMAN does keep track of media usage, so if you backed up a database using 4 streams, and then issue a restore using 8 streams, CommVault will issue the RMAN command using 8 channels, but RMAN/Oracle will only use 4 of those 8 channels since only 4 were used for the backup."

     

    Thanks

    -Anders

  • Re: Oracle restore question
    Posted: 11-06-2018, 3:53 AM

    As far as I know the maximum amount of streams allocated on a restore is determained by the amount of streams used for the backup. So that would mean that there will be 4 streams allocated in the restore, assigning more streams which do not process data will result in non efficient usage of resources allocation by the commserve. Can't imagine this would be the case, but I could be wrong.

    Curious what others have to say about this


    Jos Meijer
    Senior Technical Consultant
  • Re: Oracle restore question
    Posted: 11-06-2018, 4:14 AM

    Hi Jos.

     

    Thanks for your reply.

     

    My Oracle collegues are of the opinion, that if they start a restore with 8 oracle channels, they will get 8 channels even if the backup was done with 4 Commvault streams.

     

    So would be great if this could be confirmed or not, even with support of some documentation.

     

    Regards

    -Anders

  • Re: Oracle restore question
    Posted: 11-06-2018, 7:55 AM

    Checked documentation and interesting to see that the oracle agent is not mentioned as multi stream restore capable. This would indicate that a single stream restore is performed.

    http://documentation.commvault.com/commvault/v11/article?p=92576.htm

    Agents That Support Multi-Stream Restore Operations

    The following agents support multi-stream restore operations:


    Jos Meijer
    Senior Technical Consultant
  • Re: Oracle restore question
    Posted: 11-06-2018, 2:49 PM

    i have done the same , backup with 4 stream and restore with 8 stream

    As per RMAN log during restore it shows 8 channel allocated and restore time is also less. however in the restore job details it always shows 1 stream ( may be a bug which Commvault need to fix)

    As per my experience i did not have any issues in the restore with increase in number of streams

  • Re: Oracle restore question
    Posted: 11-07-2018, 2:22 AM

    Sunny48:

    As per RMAN log during restore it shows 8 channel allocated and restore time is also less. however in the restore job details it always shows 1 stream ( may be a bug which Commvault need to fix)

    Interesting that you can assign more streams.. Wonder why that is.

    Regarding your 1 stream shown, this is due to the agent not supporting multi stream restores.


    Jos Meijer
    Senior Technical Consultant
  • Re: Oracle restore question
    Posted: 11-08-2018, 3:33 AM

    This is the answer I got from support:

     

    "Regarding your question how many restore streams are used if you backup using 4 streams, the answer is, it will use 4 streams for restore even though you used 8 streams to do the recovery.

    The way RMAN works, you can back up a database using 8 streams, and restore/duplicate using the same 8 streams. RMAN does keep track of media usage, so if you backed up a database using 4 streams, and then issue a restore using 8 streams, CommVault will issue the RMAN command using 8 channels, but RMAN/Oracle will only use 4 of those 8 channels since only 4 streams were used for the backup."

     

    So that concludes that you can only restore with the same amount of streams as you did use for backup.

     

    Thank you all for your inputs.

     

    Regards

    -Anders

  • Re: Oracle restore question
    Posted: 11-08-2018, 7:49 AM

    Is there a way we can check the logs to confirm what they are saying is correct. The reason I am saying is i have tested both the senario and got less recovery time when i used more number of channels than backup. Also when ihave worked with CommVault support for restore issues they too selected more streams than backup.

    Sowondering if there is any logs or documents to support it

  • Re: Oracle restore question
    Posted: 11-10-2018, 12:58 PM

    Hi Sunny,

    If you have the RMAN log from the restore job, it will actually show the details of how many streams are allocated and used for RMAN restore.

     

    During the control file restore phase we use only one stream regardless of how many streams are selected. Perhaps you have looked at the job details during this phase.

    We allocate those many number of channels that are chosen in the restore job options during the job restore.

     

    Thanks,

    Sunil-

  • Re: Oracle restore question
    Posted: 11-11-2018, 8:00 PM
    • efg is not online. Last active: 03-21-2019, 11:18 AM efg
    • Top 10 Contributor
    • Joined on 02-02-2010
    • CommVault Tinton Falls NJ
    • Expert
    • Points 1,616

    This is still true.  You can allocate 8 streams/channels for the restore, and Commvault will issue the correct RMAN syntax to use 8 channels, but if only 4 streams were used for the backup, since RMAN keeps track of the media usage, it will only use 4 streams of those 8 allocated.  This is because of a feature added in Oracle 10g to prevent RMAN from requesting pieces from the same tape at the same time for restore.  Now that most backup media is disk you don't really have to worry about tape drive reservations, so there is an option in RMAN called "PARALLELMEDIARESTORE".  Setting this parameter to "OFF" (ie.  "SET PARALLELMEDIARESTORE OFF") RMAN won't check the media (barcode/lable) and should let RMAN use ALL 8 streams/channels.  To use this with Commvault you will have to customize the restore session generated by the server.  See: Customizing Oracle Restore RMAN Scripts


    Ernst F. Graeler
    Senior Engineer III
    Development
  • Re: Oracle restore question
    Posted: 12-18-2018, 3:24 PM

    hmm.. then in this case the num of channel option should have been disabled in commvault. How about the RMAN Logs for the restore? why its says channel alocated and relewase if in the background only chanelles used for backup is used.

     

     

  • Re: Oracle restore question
    Posted: 12-18-2018, 3:44 PM
    • efg is not online. Last active: 03-21-2019, 11:18 AM efg
    • Top 10 Contributor
    • Joined on 02-02-2010
    • CommVault Tinton Falls NJ
    • Expert
    • Points 1,616

    We don't disable the number of channels as it is possible to use more or less channels that were used for the backup.   As I stated in my post, RMAN still allocates the channels, but unless the "PARALLELMEDIARESTORE" option is set it will only use the same number of channels or less than were used for the backup.  As far as only seeing one stream in the job details while the restore is running, there is a known issue in Commvault where only one stream is displayed for ANY agent.

    Let us know if this helps explain what you are seeing.


    Ernst F. Graeler
    Senior Engineer III
    Development
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