Windows Azure Storage (WAS)

Brad Calder delivering SOSP talk

Since its initial release, Windows Azure has offered a storage service known as Windows Azure Storage (WAS). According to the SOSP paper and related talk published by the team (led by Brad Calder), WAS is architected to be a “Highly Available Cloud Storage Service with Strong Consistency.” Part of being highly availably is keeping your data safe and accessible. The SOSP paper mentions that the WAS service retains three copies of every stored byte, and (announced a few months before the SOSP paper) another asynchronously geo-replicated trio of copies in another data center hundreds of miles away in the same geo-political region. Six copies in total.

WAS is a broad service, offering not only blob (file) storage, but also a NoSQL store and a reliable queue.

Further, all of these WAS storage offerings are strongly consistent (as opposed to other storage approaches which are sometimes eventually consistent). Again citing the SOSP paper: “Many customers want strong consistency: especially enterprise customers moving their line of business applications to the cloud.” This is because traditional data stores are strongly consistent and code needs to be specially crafted in order to handle an eventually consistent model. This simplifies moving existing code into the cloud.

The points made so far are just to establish some basic properties of this system before jumping into the real purpose of this article: performance at scale. The particular points mentioned (highly available, storage in triplicate and then geo-replicated, strong consistency, and supporting also a NoSQL database and reliable queuing features) were highlighted since they may be considered disadvantages – rich capabilities that may be considered to hamper scalability and performance. Except that they don’t hamper scalability and performance at all. Read on for details.

Performance at Scale

A couple of years ago, Nasuni benchmarked the most important public cloud vendors on how their services performed on cloud file storage at scale (using workloads modeled after those observed from real world business scenarios). Among the public clouds tested were Windows Azure Storage (though only the blob/file storage aspect was considered), Amazon S3 (an eventually consistent file store), and a couple of others.

In the first published result in 2011, Nasuni declared Amazon S3 the overall winner, prevailing over Windows Azure Storage and others, though WAS fininshed ahead of Amazon in some of the tests. At the time of these tests, WAS was running on its first-generation network architecture and supported capacity as described in the team’s published scalability targets from mid-2010.

In 2012, Microsoft network engineers were busy implementing a new data center network design they are calling Quantum 10 (or Q10 for short). The original network design was hierarchical, but the Q10 design is flat (and uses other improvements like SSD for journaling). The end result of this dramatic redesign is that WAS-based network storage is much faster, more scalable, and as robust as ever. The corresponding Q10 scalability targets were published in November 2012 and show substantial advances. EDIT: the information on scalability targets and related factors is kept up to date in official documentation here.

Q10 was implemented during 2012 and apparently was in place before Nasuni ran its updated benchmarks between November 2012 and January 2013. With its fancy new network design in place, WAS really shined. While the results in 2011 were close, with Amazon S3 being the overall winner, in 2012 the results were a blowout, with Windows Azure Storage being declared the winner, sweeping all other contenders across the three categories.

“This year, our tests revealed that Microsoft Azure Blob Storage has taken a significant step ahead of last year’s leader, Amazon S3, to take the top spot. Across three primary tests (performance, scalability and stability), Microsoft emerged as a top performer in every category.” -Nusani Report

The Nasuni report goes on to mention that “the technology [Microsoft] are providing to the market is second to none.”

Reliability

One aspect of the report I found very interesting was in the error rates. For several of the vendors (including Amazon, Google, and Azure), Nasuni reported not a single error was detected during 100 million write attempts. And Microsoft stood alone for the read tests: “During read attempts, only Microsoft resulted in no errors.” In my book, I write about the Busy Signal Pattern which is needed whenever transient failures result during attempts to access a cloud service. The scenario described in the book showed the number of retries needed when I uploaded about four million files. Of course, the Busy Signal Pattern will still be needed for storage access and other services – not all transient failures can be eliminated from multitenant cloud services running on commodity hardware served over the public internet – and while this is not a guarantee there won’t be any, it does bode well for improvements in throughput and user experience.

And while it’s always been the case you can trust WAS for HA, these days it is very hard to find any reason – certainly not peformance or scalability – to not consider Windows Azure Storage. Further, WAS, S3, and Google Storage all have similar pricing (already low – and trending towards even lower prices) – and Azure, Google, and Amazon have the same SLAs for storage.

References

Note that the Nasuni report was published February 19, 2013 on the Nasuni blog and is available from their web site, though is gated, requiring that you fill out a contact form for access. The link is here: http://www.nasuni.com/blog/193-comparing_cloud_storage_providers_in

Other related articles of interest:

1. Windows Azure beats the competition in cloud speed test – Oct 7, 2011 – http://yossidahan.wordpress.com/2011/10/07/windows-azure-beats-the-competition-in-cloud-speed-test/
2. Amazon bests Microsoft, all other contenders in cloud storage test – Dec 12, 2011 –
3. Only Six Cloud Storage Providers Pass Nasuni Stress Tests for Performance, Stability, Availability and Scalability – Dec 11, 2011 – http://www.nasuni.com/news/press_releases/46-only_six_cloud_storage_providers_pass_nasuni_stress
4. Dec 3, 2012 – http://www.networkworld.com/news/2012/120312-argument-cloud-264454.html – Cloud computing showdown: Amazon vs. Rackspace (OpenStack) vs. Microsoft vs. Google
5. http://www.networkworld.com/news/2013/021913-azure-aws-266831.html?hpg1=bn – Feb 19, 2013 – Microsoft Azure overtakes Amazon’s cloud in performance test