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.
How is having geo-replication great when failing over is out of our hands and is at the discretion of Microsoft?
Thanks for posting your question. There are two big advantages - the first is cost and the other is transparency. Geo-replication with Windows Azure Storage (WAS) is a lot less expensive than doing it yourself with your own storage hardware that you manage and operate yourself in your own secondary data center. The transparency of the failover means that you don't even know that a failover is occurring.
This is different than a traditional (Non-cloud) DR system where there are two sets of hardware in different data centers and the IT team periodically fails over from one site to another as a way of testing their failover technology and processes. This level of DR protection tends to be expensive and takes a great deal of planning and effort from the IT team. Cloud-based DR will probably not replace traditional DR for low-latency teir 1 transaction processing applications because the traditional approach provides minimal loss for transactions that were in-flight between data centers. However, there are many applications that do not need this level of protection that can use Hybrid Cloud Storage for cloud snapshots, archiving and tiering where Azure's Geo-replication is extremely effective and affordable. Remember too that WAS makes three copies of data in three different local domains before the Geo-replication step. This is a lot of redundancy, but the point of it is to make customers feel secure.