Slow tape verification speed.

Last post 07-31-2019, 8:44 AM by Wwong. 4 replies.
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  • Slow tape verification speed.
    Posted: 07-26-2019, 10:00 AM

    Currently running Commvault v11 on a Server 2012 R2 VM.  We have a separate media agent with a Dell EMC ML3 tape loader attached to it consisting of two LTO-7 FC drives.  On the aux copy to tape we get anywhere between 800-2000GB/hr with the two drives running concurrently but we seem to be hovering around 500GB/hr sustained on the verification (which I would expect to go much faster due to compression).  Looking for advice on how to approach this.  I already have the latest firmware and drivers on the server/unit (and per previous troubleshooting tickets we have changed the autoloader driver to "Unknown Medium Changer").  Antivirus (McAfee) doesn't appear to be interferring.  There are also zero read/write errors logged for either drive thus far.


    Nothing appears to be "wrong", it's just consistently slow for no reason (certainly when compared to the write speed).  Really curious if this might be a result of a misconfiguration of Commvault or the storage policy, but if it was I would really expect that to manifest itself in the write speed as well. Thanks in advance.

  • Re: Slow tape verification speed.
    Posted: 07-29-2019, 8:04 AM

    Hi J D 

    Can you please share how the Secondary Copy configuration is done, is "Combine Source Stream" or Multiplexing enabled?

    Although Aux Copy to Tape is achieving very good write throughput, Read performance could differ depending on the above setting



  • Re: Slow tape verification speed.
    Posted: 07-29-2019, 10:26 AM

    I have it set to combine streams to two (two tape drives in the autoloader) but I do not have multiplexing enabled.  Could that be a factor?

  • Re: Slow tape verification speed.
    Posted: 07-29-2019, 11:06 AM

    I did a validate drive and I'm getting about 230MB/s for write and 297MB/s for read (50 x 2GB chunks tested).  Seems like the drives/drivers are fine.  I can try not combining the streams to see if that makes a difference.  Just curious if that could be issue before doing so.

  • Re: Slow tape verification speed.
    Posted: 07-31-2019, 8:44 AM

    Hi JD 

    With combine source data stream, it allows for better optimization in Tape Media utilization as you are distributing the Secondary Copy data across two Tape Medium

    However because we are spreading the data across the two Media, and base on the rules of Aux Copy - During an Auxiliary Copy operation, the data is copied in the following sequence:

    1. A media which contains oldest backup job is copied first.
    2. When all the data from this media is copied, the other media with oldest backup job is selected for the copy from a drive pool.
    3. When all the media from the drive pool are copied, the oldest media from the other drive pool is selected for the copy.
    4. When all the media from a library are copied, the oldest media from the other library is selected for the copy.
    5. When all media associated with a MediaAgent are copied, the oldest media from the other MediaAgent is selected for the copy.

    Not every stream will be even.

    Additionally because Tape Media is sequential medium, the read process to verify the data could be slower due to the overhead to determine where the exact block is written to for the specific backup job that is Aux Copied to Tape. 

    If you attempt to do combine source stream to a single tape, and Aux Copy one backup to Tape, I would believe the verification will be faster



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