Though they may look quite similar, real differences exist among the major public cloud storage provider offerings, so you need to carefully assess services upfront and evaluate them against your particular storage requirements.
Start by looking at service terms and capabilities, which can vary by provider. To get a feel for the level of service commitments a provider is willing to make on your behalf, review its service-level agreement (SLA) and the frequently asked questions section on each provider's website. You can then narrow the list of provider candidates based on which ones come closest to meeting your workload and service-level requirements.
A rough analysis of the costs you're likely to incur is next. Storage service costs can fall into several categories, depending on whether you're looking at block storage or object storage. For example, in the case of Amazon Web Services (AWS) Elastic Block Storage (EBS), you'll pay a few cents per month for each gigabyte of standard provisioned storage and for every million input/output requests made against your standard EBS volumes. The corresponding charges for "provisioned IOPS volumes" (designed for low latency and a minimum level of IOPS) are a bit higher. If you elect to periodically snapshot your EBS volumes to Amazon Simple Storage Service (S3), you'll pay a few cents per month per gigabyte of data stored.
One example of object storage pricing is the way Amazon charges differently for each class of S3 storage (standard versus reduced redundancy). There are specific monthly costs for the number and size of objects stored, the number and type of object operational requests (Get, Put, Copy and so on) made via the REST application programming interface, and the amount of data transferred out of a given S3 region. These storage costs may seem insignificant in the beginning, but they can add up quickly as your AWS storage installation grows.
If you're considering running key applications and/or data sets in the public cloud, you should try to talk with customers of each cloud storage provider's service. In this instance, strongly consider paying for support services, since your workloads and associated storage won't tolerate excessive downtime or other service issues. For example, Amazon now offers several tiers of premium support, with services geared toward developers, midsize businesses and enterprise customers. You can speak with technically savvy support representatives with guaranteed response times, receive guidance on best practices, and access diagnostic tools and architectural and operational consulting resources to support your own AWS infrastructure development or expansion efforts. Cloud storage support services can be a bit pricey, especially for high-volume customers, but will likely be worth the money if you're running important workloads or managing key infrastructure initiatives on a public cloud site.
Once you've scoped out the basic costs and terms of each cloud provider's service, you can probe for more details about overall storage service capabilities. To assist in that effort, these seven questions should provide you with the answers you need during your due diligence process:
1. How easy is it to import data into the cloud storage service?
2. How secure will my data be, both in motion and at rest? (Look for evidence of physical/facilities security as well as firewalls, data encryption and access controls.)
3. What provisions, if any, are in place to protect and preserve my data, e.g., via replication across availability zones and/or regions?
4. How many 9s of availability does the provider's SLA guarantee? How is the term availability defined, and what kind of credits (or other compensation) will I receive in the event of downtime?
5. What about traditional data protection? Are snapshot and/or backup services provided?
6. What will my total monthly cost likely be, including all charges on the provider's rate card?
7. In the event I decide to terminate the cloud storage service, what is the process and cost for moving my data back to my data center or to a different provider's site? How can I be sure that all of my data has been fully deleted upon exit?
You should be satisfied with the answers to each of these questions before making a decision on a specific cloud storage provider and service. If you do your homework in advance, you're much more likely to be happy with your public cloud storage experience.