Cloud storage is a model of networked online storage where data is stored in virtualized pools of storage which are generally hosted by third parties. Hosting companies operate large data centers, and people who require their data to be hosted buy or lease storage capacity from them. The data center operators, in the background, virtualize the resources according to the requirements of the customer and expose them as storage pools, which the customers can themselves use to store files or data objects. Physically, the resource may span across multiple servers.

Cloud storage services may be accessed through a web service application programming interface (API), a cloud storage gateway or through a Web-based user interface.

Advantages

• Companies need only pay for the storage they actually use as it is also possible for companies by utilizing actual virtual storage features like thin provisioning.
• Companies do not need to install physical storage devices in their own datacenter or offices, but the fact that storage has to be placed anywhere stays the same (maybe localization costs are lower in offshore locations).
• Storage maintenance tasks, such as backup, data replication, and purchasing additional storage devices are offloaded to the responsibility of a service provider, allowing organizations to focus on their core business, but the fact stays the same that someone has to pay for the administrative effort for these tasks
• Cloud storage provides users with immediate access to a broad range of resources and applications hosted in the infrastructure of another organization via a web service interface.
• Cloud storage can be used for copying virtual machine images from the cloud to on-premise locations or to import a virtual machine image from an on-premise location to the cloud image library. In addition, cloud storage can be used to move virtual machine images between user accounts or between data centers.

Issues

• When data is distributed it is stored at more locations increasing the risk of unauthorised physical access to the data. For example, in cloud based architecture, data is replicated and moved frequently so the risk of unauthorised data recovery increases dramatically. (e.g. disposal of old equipment, reuse of drives, reallocation of storage space) The manner that data is replicated depends on the service level a customer chooses and on the service provided. Different cloud vendors offer different service levels. Risk of unauthorized access to data can be mitigated through the use of encryption, which can be applied to data as part of the storage service or by on-premises equipment that encrypts data prior to uploading it to the cloud.
• The number of people with access to the data who could be compromised (i.e. bribed, or coerced) increases dramatically. A single company might have a small team of administrators, network engineers and technicians, but a cloud storage company will have many customers and thousands of servers and therefore a much larger team of technical staff with physical and electronic access to almost all of the data at the entire facility or perhaps the entire company.[citation needed] Encryption keys that are kept by the service user, as opposed to the service provider limit the access to data by service provider employees.
• It increases the number of networks over which the data travels. Instead of just a local area network (LAN) or storage area network (SAN), data stored on a cloud requires a WAN (wide area network) to connect them both.
• By sharing storage and networks with many other users/customers it is possible for other customers to access your data. Sometimes because of human error, faulty equipment, a bug and sometimes because of criminal intent. This risk applies to all types of storage and not only cloud storage. The risk of having data read during transmission can be mitigated through encryption technology. Encryption in transit protects data as it is being transmitted to and from the cloud service. Encryption at rest protects data that is stored at the service provider. Encrypting data in an on-premises cloud service on-ramp system can provide both kinds of encryption protection,

Vendors
The cloud seems made for online storage. At its core, the cloud offers a nearly infinite space to store data, whether it's for backup, business continuity, disaster recovery or any of the other myriad purposes. And for solution providers, offering Storage-as-a-Service, or offering the ability to back up or store data via the Internet, is creating new business opportunities. The ability to dynamically expand or scale back storage capacity on demand is a powerful proposition, and solution providers and enterprises want to ensure they're trusting their data to the right cloud storage vendor.

• 3Xsystems     With its marquee product, the 3X Backup system, 3X delivers online backup service in a cheap, portable and all-in-one device end customers can buy through the channel, giving the user an added local resource to tackle data continuity and backup.
• Amazon     It set the stage with its cloud infrastructure, and Amazon Web Services continued its dominance with Simple Storage Service (S3), its cloud storage service that offers users massive amounts of cloud storage for short money in Amazon's cloud.
• Asigra     Public or private cloud? Asigra's got you covered. The company offers a Public Cloud Backup Service or Private Cloud Backup Solution to cover the backup bases in both types of environments, and it requires no agent to back up data on your servers.
• Axcient     Axcient pulls double duty. The company offers data protection and business continuity for MSPs with a hybrid on-premise appliance for backup and combines that with its cloud-based disaster recovery service. What's more, it's pay-as-you-grow and features no infrastructure, license or software costs.
• Carbonite     Carbonite started in the cloud when one founder's daughter's hard drive crashed and the other's wife's laptop was stolen. Now, Carbonite offers unlimited cloud backup at flat rates and has backed up more than 80 billion and restored more than 7.2 billion files.
• Caringo     Caringo's flagship CAStor software is a unified object storage operating system that runs on standard x86 hardware and is a massively scalable foundation for cloud storage applications, secondary storage that complements SAN and NAS, or for simple and affordable data archiving.
• Cleversafe     Cleversafe fires on all cloud storage cylinders to address storage requirements with tight security, protection and scalability. Public, private and hybrid clouds all get their due whether it's for archive storage, accessible backup, content distribution or a host of other use cases.
• ctera     Targeting the SMB and the branch office with its Cloud Attached Storage play, a hybrid solution that marries cloud storage services with on-premise appliances, resellers have the tools to offer cloud storage, hybrid local and off-site data protection and collaboration as a managed service.
• Doyenz     Doyenz gives IT providers a suite of cloud-based disaster recovery services to ensure reliable backups and seamless virtual failover. With its Shadowcloud, an active image of the production server is kept in the cloud for use at all times, giving clients immediate continuity.
• eFolder     eFolder offers high-assurance data protection services for remote and local backup and e-mail archiving through its massive stable of VARs and MSPs. Its backup technology uses a reverse-delta technology.
• i365     Seagate-owned i365 stores to the cloud with its portfolio of EVault cloud-connected backup and recovery products and services. With EVault SaaS, EVault SaaS Remote Disaster Recovery and EVault SaaS Managed Services, i365 has various flavors of cloud storage for any appetite.
• Intronis     Intronis has been in the cloud since 2003 with its backup and disaster recovery services for MSPs. The company uses 256-bit AES security and multiple data centers on opposite coasts to protect data and ensure availability.
• Mezeo     Mezeo's cloud storage platform offers a service-enabled platform that is easy to deploy, is multitenant, highly scalable and secure. The Mezeo Cloud Storage API and Interoperability API help service providers monetize Storage-as-a-Service with their own branded offerings.
• Nasuni     Nasuni prides itself as the gateway to cloud storage and a vendor that makes cloud storage a reality for businesses. With its Nasuni Filer, a virtual NAS file server, Nasuni leverages cloud resources to ease file storage and protection in the midmarket.
• Nirvanix     Security, reliability and redundancy take center stage for Nirvanix. With its CloudComplete portfolio, Nirvanix gives its users a host of cloud storage deployment options that includes the CloudNAS Gateway, the public cloud Storage Delivery Network, and hNode hybrid and private cloud solutions.
• Scality     Scality is sick of storage system sprawl management, failures, limitations and manual intensive data migration; and with its Scality RING software the company looks to transform commodity x86 server hardware and Ethernet LANs into cloud storage, all while chopping costs.
• Storsimple     StorSimple has made waves as an application-optimized cloud storage player for Microsoft Server applications. The company is bent on bringing the benefits of the cloud to on-premise applications without forcing customers to migrate those applications to the cloud.
• SugarSync     SugarSync's online backup, file sync, and sharing service makes it easy to stay connected. With SugarSync you get secure cloud storage for all your files — documents, music, photos, and videos.
• Vembu     Vembu attacks the cloud storage market with a suite of online, hybrid and cloud-based storage products and services: Vembu Pro online backup service; Vembu Home cloud storage service; StorGrid SP Edition online backup software; and StorGrid Pro Edition hybrid backup software.