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Storage Replica write ordering

    Frage

  • https://docs.microsoft.com/en-us/windows-server/storage/storage-replica/stretch-cluster-replication-using-shared-storage

    ...says:

    Leave the Consistency Group value at Highest Performance if you do not plan to use write ordering later with additional disk pairs in the replication group. If you plan to add further disks to this replication group and you require guaranteed write ordering, select Enable Write Ordering, and then click Next.

    Can I ask...

    If I only need multiple separate single source data volumes to be asynch (not fully synch) replicated, then is:

    1) is there an increased risk of not being able to mount the replica target (after source site loss) due to NTFS meta-data not being fully up to date... I mean I get the concept that some write IOs might not have made it off-site, but will I be exacerbating the problem by not selecting "enable write ordering" ?

    2) is there a performance impact from having, or not having, enable write ordering - for a single volume replications ?Thanks.

    Dave.

    Mittwoch, 16. Mai 2018 12:53

Alle Antworten

  • Hi Dave,

    According to the description from the Wizard, Consistency groups control application IO writing.

    Write ordering ensures that write orders across disks are maintained during the replication which ensures in the even of a failover the disks are still in a consistent state and safe from any corruption caused by writes out of sequence across disks.

    If there's large data writing IO, it is suggesting you enable Write ordering. For single volume, from my personal viewer, the impact is  inapparent. But I haven't find the official documents from Microsoft, I suggest you could do a test in your lab.  I'm afraid that you may need to choose it based on your own environment.

    In addition, here is an example about deploy Stretch Cluster with Volume Replication, you could take a look

    https://www.starwindsoftware.com/blog/how-to-configure-storage-replication-using-windows-server-2016-part-2

    Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

    Best Regards,

    Mary


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    Donnerstag, 17. Mai 2018 02:49
    Moderator
  • Thanks for the reply Mary.

    That starwind article looks promising, but really it's not a proper four node stretch cluster with two nodes in each of two different AD sites or subnets.

    I have set-up a test of a four node cluster, two pairs, and have SR replicating, but my initial test platform didn't have separate AD sites, and I only had the one VLAN to work in, so I couldn't create a proper stretch cluster either (not yet)... my next test will be an attempt to build a proper stretch cluster between two sites, and in two different subnets.

    Anyway...

    ...back to the question of write-ordering.

    I can see how write ordering is of interest when multiple "pairs / sets" of data volumes need to be replicated, e.g. SQL databases on E: and SQL logs on F:...

    ...but at this time I want to limit my question perhaps to something like this...

    ...if I have only one data volume E: (and my Storage Replica log volume is F:) then if multiple applications/users/threads/jobs/processes are all creating/opening/closing/reading/writing/deleting many files across many folders and therefore lots of NTFS bitmap changes and NTFS MFT and NTFS meta-data writes are also occurring at the same time... then... I think my questions are:

    1) Does write-ordering  enabled/disabled   even have any effect with a single Storage Replica data volume?  i.e. maybe all writes to a single Storage Replica volume are always in order anyway ?

    2) If "write-ordering disabled" is a valid state for a asynch Storage Replica with a single Storage Replica data volume, then are my chances increased for a corrupt Storage Replica target data volume, when brought online at the target site?

    Or should I open a support case?

    Thanks again.

    Dave.

    Donnerstag, 17. Mai 2018 16:50
  • Hi Dave,

    I'm afraid for dedicated Support about such performance analysis you might need to contact  Microsoft Customer Support Services (CSS).

    It is also appreciated that the other members in our forum can share their experience with us about this scenario.

    To obtain the phone numbers for specific technology request, please refer to the website listed below:

    https://www.microsoft.com/en-us/worldwide.aspx

    Appreciate your support and understanding.

    Best Regards,

    Mary


    Please remember to mark the replies as answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.

    Freitag, 18. Mai 2018 01:56
    Moderator