the effect of Block level Deduplication factor on DASH copies

Last post 01-20-2020, 8:14 PM by Anthony.Hodges. 1 replies.
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  • the effect of Block level Deduplication factor on DASH copies
    Posted: 01-20-2020, 5:11 PM

    The default/recommended block size for deduplicated storage policies is 128KB….except for storage policies “associated with cloud storage libraries,” where the recommended block size is 512KB.

    Accordingly, we have storage policies where the primary copy on a local disk library is configured with a deduplication policy block size of 128KB and a secondary copy on cloud storage with a deduplication policy block size of 512KB.

    But when I think about Aux copies, it seems to me that different block size will force all data to be transmitted, and new deduplication signatures generated for all data copied to the secondary cloud storage copy.   Two different sized blocks will neve have the same deduplication signature.    And so to be able to use DASH copies effectively, the primary and secondary copies must have deduplication policies with the same block size.

    Does this make sense, or am I missing something?

  • Re: the effect of Block level Deduplication factor on DASH copies
    Posted: 01-20-2020, 8:14 PM

    Hi CarlosG,

    For differing block sizes, Commvault recommend using the Network Optimized and not Disk Optimized DASH.  For network optimized the data is read on the 128kB side and a 64B signature is generated based on the destination 512kB block size.  This does incur a bit of a read penalty on the source side as this process involves rehydration.

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