Aux copy slow

Last post 07-22-2010, 7:21 AM by sean. 3 replies.
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  • Aux copy slow
    Posted: 07-19-2010, 7:16 PM

    Hi, we are running v8.0 with deduplication on windows file system backups.  The aux copy for this job runs very slow - only about 38GB/hr.   Other aux copies are nearly twice as fast at about 70GB/hr. 

    Any ideas on where to start the troubleshooting?

  • Re: Aux copy slow
    Posted: 07-20-2010, 12:22 AM

    Hi swmacdonald,

    There are a few things to consider:

    1. Is this aux copy using the same resources as the other "fast" copies?
    I.e. same media agents, same disk resources etc.

    2. Do your other copies/policies have dedupe enabled?

    3. are you copying from dedupe disk to tape (always non dedupe) , or to another dedupe disk copy, or to a non dedupe disk?

    If you start by creating a quick list of the paths your data takes for different aux copies, you should be able to see if there is anything which may stand out.

    Cheers,

    Will

  • Re: Aux copy slow
    Posted: 07-21-2010, 12:12 AM

    When you perform an aux copy of a Dedup job, you actually 'rehydrate' (unravel or explode) the data back to a non-dedup state. As a result.. this causes a lot of very random read IO, and can impact disk read performance in a very big way if you are using SATA as the aux copy source.

    You could try to enable multiplexing to increase the the overall throughput, however this may compound the workload issue for the SATA, and make matters worse potentially. Results will be better or worse depending on your storage environment.

    SATA disks generally work best when you use them for sequential IO (not random).

    Commvault may recommend using SILO backups if that suites, which keeps the data deduplicated all the way to tape (and keeps the SATA read workload sequential).

    http://documentation.commvault.com/commvault/release_8_0_0/books_online_1/english_us/features/single_instance/single_instance.htm#Auxiliary_Copy_and_Synthetic_Full_Backups

    Auxiliary Copy

    Auxiliary Copy operations will automatically unravel or explode a deduplicated data. In the case of Auxiliary Copy, if the secondary copy is set up for Deduplication, then the deduplication store gets created for the copy and the associated data is deduplicated for secondary copy. The Auxiliary copy follows the deduplication type (both block level and object level) of the Source Copy.

     
    • Data in a storage policy copy enabled for Deduplication can not be multiplexed. Therefore, Data Multiplexing is not supported if the storage policy copy is enabled with Deduplication. However, a SILO copy supports Data Multiplexing even if the storage policy copy is enabled with Deduplication.
    • Multiplexed data cannot be copied to a storage policy copy enabled for Deduplication. Therefore, a storage policy copy enabled for Deduplication can not have a direct or indirect source copy enabled for Data Multiplexing.
    • An Auxiliary Copy can be configured with Data Multiplexing when the source copy is enabled for Deduplication.
  • Re: Aux copy slow
    Posted: 07-22-2010, 7:21 AM

    hi, may i tab this to ask related to auxcopy matter: Having a Media agent host provisioned with external LUN01 (primary magnetic lib), and then external LUN02 (auxcopy magnetic lib). While auxcopy job is running, is the data flow happens between LUN01 -> LUN02? Or LUN01 -> MA host (HBA device) -> LUN02?

    Thanks..

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