On December 5th Microsoft announced a pricing reduction for Windows Azure Storage. One of the more noticeable aspects of the announcement was the breakdown of storage costs between Geo Replicated Storage and Locally Redundant Storage. To summarize, Geo Replicated Storage costs approximately 28% more for the additional service of replicating your data to a remote secondary Azure data center. When you understand the details of how data Azure Storage works it means there are six copies of data stored - three locally and three remotely. This is an example of an extremely robust design where an awful lot has to go wrong to lose data and it is part of the reason why Windows Azure Storage has such an excellent track record.
If you are considering a Hybrid Cloud Storage solution using StorSimple Cloud-integrated Storage (CiS) and Windows Azure Storage, my advice is that you plan to use Geo Replicated Storage. The additional 28% price premium for Geo Replication is a small amount to pay for remote replication with automated failover. If you compare the cost for Azure's Geo Replication with other forms of data replication that conservatively double the cost of storage, it is an incredible bargain.
So here is how the connections and data flows work with a CiS Hybrid Storage Cloud. Thanks to Avkash Chauhan for posting about this previously in his blog -the graphic below came from there.
When data is uploaded by the on-premises CiS solution to Azure Storage, three copies of the data are written to separate domains within the primary data center and an acknowledgement is sent to the CiS on-premises. Some time afterwards, which can be several minutes later, the data is replicated to the secondary data center and another three copies are written to three different domains there. This is done transparently in the background, without involving the CiS system in any way.
With CiS-powered Hybrid Cloud Storage, uploads to Windows Azure Storage occur when nightly CiS Cloud Snapshots are taken but they also happen when inactive data it is tiered to Azure Storage. Under normal conditions, the amount of traffic between CIS on premises and Azure Storage is negligible. Exceptions to that occur during the initial Cloud Snapshot for a volume when the entire volume's data is snapped or during DR scenarios when a lot of data may need to be downloaded from Azure Storage to CiS. If you are concerned about the amount of bandwidth that might be consumed by Hybrid Cloud Storage traffic, CiS provides scheduled bandwidth throttling. Many of our customers use it to assure they have all the bandwidth they need for other production applications. Geo Replication between Azure data centers does not consume bandwidth between the customer site and the primary Azure data center, so there is no need to avoid Geo Replication in order to conserve bandwidth.
When you think about the economics of cloud storage, make sure to include the incredible value of Geo Replication.