Factors That Will Impact the Public Versus Private DecisionInitial InvestmentThere is often an assumption that private clouds require a million dollar capital outlay and investment in racks and racks of equipment. The reality is that private clouds can be built for under $5,000 and deployments are simple. Users can download software and have a cloud running in under an hour.
Public clouds can start as low as $100. Since there is no hardware or software to purchase, the initial investment is trivial assuming your applications can speak the required protocols.
Amount of Data
Cloud storage is known for its massive scalability but most companies start out small. Private clouds can start in the few TB range and provide easy scale out of capacity by adding additional nodes or disks.
Public clouds start even smaller. For example, a public cloud makes it easy to back up a single laptop or deploy an application starting at a few GBs. As you grow you can lease more capacity and the cost scales linearly.
Longevity of Data
How long you plan on keeping data in the cloud can greatly impact your selection. As data ages within the public cloud, the cost continues to rise. If you are publishing frequently changing or short-lived content, such as movie trailers or daily newscasts, the flexibility of a public cloud is a good solution.
Private clouds are licensed like enterprise. Longevity of data does not increase the cost of the solution, which bodes well for archive or content repository applications.
Required Performance
Private clouds are deployed inside the firewall and accessed over the Ethernet LAN at wire speed. Read access in the 100 MB/s range per node is not uncommon. Adding nodes provides additional performance to the cloud. Files can be replicated to many nodes, each of which can serve requests independently.
Public clouds are accessed over the Internet and face the limits of your and the providers bandwidth connection. This usually caps out around 10MB/s. To scale performance you can initiate additional 10MB/s connections but doing so increases the bandwidth charges.
Access Patterns and Locations
Public cloud offerings typically include replication of data to multiple geographically dispersed locations, sometimes for an extra fee. If your users are global and can benefit from locality of data, a public cloud can sometimes substitute for a content distribution network.
Private clouds are typically deployed in a single location for LAN-based access. Remote users will need to connect over the WAN and work with Internet-type latencies. Larger private cloud deployments can include multiple locations and start to approach the public cloud distribution, albeit at a higher initial investment.
Security and Data Isolation
There are many published opinions and dedicated websites that cover security of public cloud offerings. The bottom line is it comes down to control of your data. Public clouds are just that, public. Isolation of data is only as strong as the virtualization technologies used to build the cloud and the provider's firewall. If you are concerned about the data being outside of your company, it should not be in a public cloud.
Private clouds are owned, deployed and managed by internal employees. Data is isolated based on your requirements and security is based on internal processes.
Confidentiality and Destruction of Data
Similar to security, confidentiality of data is a factor to consider when choosing a cloud storage solution. The law is defined based on control of the data. If the service provider is subpoenaed for your data based on their control of the data, they must comply regardless of your knowledge or objections.
With private clouds you maintain control and have input, or at least knowledge of, legal activities. When it comes time to destroy or delete the data, it is in your power and can be confirmed by your own team.
Service Level Agreements
Private clouds have different mechanisms for data availability and service of access. Most leverage multiple copies of files on multiple nodes and treat each node as a failure domain. Individual server failures do not bring down the cloud or create data loss, so most SLA agreements are satisfied. Be sure to have a complete understanding of the architecture and its capabilities when selecting and deploying a private cloud.
Public cloud SLAs are published by the provider and are their responsibility. Remediation is typically a cash payment and while they will do their best to recover data, there is no guarantee of data availability. SLAs can also be impacted by Internet connectivity. If your link goes down, you cannot access your data and there is no remediation (unless your network provider has guaranteed uptime).
In-House Technical Resources
Public clouds remove the need for server and storage administrators. Data center space and associated costs are removed, enabling businesses to focus on core competencies, although not all technical resource requirements go away. Many public offerings use newer protocols such as WebDav or REST for access. If your applications do not support this protocol, it will require changes in process, code, and/or technical staff.
Deployed inside the firewall, private clouds require system administrators but at a scale that dwarfs existing NAS standards. A single system administrator can easily manage a 100-node cloud with a part-time effort. Private clouds leverage widely deployed standards, such as NFS or CIFS, removing the need for custom application development.
How Do I Choose?
Choosing the appropriate solution is not an exercise in rocket science and comes down to a basic understanding of your data and usage. Apply the above criteria to your use case and the answer will emerge.
Cloud computing is a game changer. The cloud ...
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