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Consistency Levels in Azure Storage RRS feed

  • Question

  • Hi,

     

    I would like to know what consistency and concurrency levels do each of the following items provide:

    - Azure Tables

    -page blobs

    -block blobs

    -SQL Azure

    I suppose Drives follow blobs in terms of consistency and possibility of concurrent access.

     

    Thanks!

    Jalal


    Jalal
    Tuesday, April 19, 2011 11:03 PM

Answers

  • Azure Storage uses strong consistency with (ETag-based) optimistic concurrency for blobs and tables. Once written, a blob or entity will always return precisely the same value until it is updated by another storage operation. Only one instance can mount an Azure Drive for write.

    The following is documented for SQL Azure:

    Both the READ_COMMITTED_SNAPSHOT and ALLOW_SNAPSHOT_ISOLATION database options are set to ON in SQL Azure Database.

    • Marked as answer by Brad Calder Saturday, April 23, 2011 8:45 AM
    Tuesday, April 19, 2011 11:50 PM
    Answerer

All replies

  • Azure Storage uses strong consistency with (ETag-based) optimistic concurrency for blobs and tables. Once written, a blob or entity will always return precisely the same value until it is updated by another storage operation. Only one instance can mount an Azure Drive for write.

    The following is documented for SQL Azure:

    Both the READ_COMMITTED_SNAPSHOT and ALLOW_SNAPSHOT_ISOLATION database options are set to ON in SQL Azure Database.

    • Marked as answer by Brad Calder Saturday, April 23, 2011 8:45 AM
    Tuesday, April 19, 2011 11:50 PM
    Answerer
  • Thank you for the response!

    Regarding Azure Drive,

    - Is it possible that two instances mount a drive for read?

    - Can you please explain in more details. What sort of consistency or concurrency protocol does it follow? (i.e. does it follow a lock-based concurrency model?)

     

    Thanks!


    Jalal
    Sunday, April 24, 2011 9:12 PM
  • - Is it possible that two instances mount a drive for read?

    Yes. Create a snapshot of the VHD page blob. You can then mount the snapshot read-only in more than one instance.

    Sunday, April 24, 2011 9:56 PM
    Answerer