Cloud Computing, like any computing, is a combination of CPU, memory, networking, and storage. Infrastructure as a Service (IaaS) platforms allow you to store your data in either Block Storage or Object Storage formats.
Understanding the differences between these two formats – and how they can sometimes be used together – can be a critical part of designing an overall storage profile. And the relatively low costs of cloud storage, along with its durability and high availability, can make it attractive even for local infrastructure projects.
What is Block Storage?
Block storage devices provide fixed-sized raw storage capacity. Each storage volume can be treated as an independent disk drive and controlled by an external server operating system. This block device can be mounted by the guest operating system as if it were a physical disk. The most common examples of Block Storage are SAN, iSCSI, and local disks.
Block storage is the most commonly used storage type for most applications. It can be either locally or network-attached and are typically formatted with a file system like FAT32, NTFS, EXT3, and EXT4.
Use cases

Ideal for databases, since a DB requires consistent I/O performance and low-latency connectivity.
Use block storage for RAID Volumes, where you combine multiple disks organized through stripping or mirroring.
Any application which requires service side processing, like Java, PHP, and .Net will require block storage.
Running mission-critical applications like Oracle, SAP, Microsoft Exchange, and Microsoft SharePoint.

Block storage options in the cloud

AWS Elastic Block Storage (EBS): Amazon EBS provides raw storage – just like a hard disk – which you can attach to your Elastic Cloud Compute (EC2) instances. Once attached, you create a file system and get immediate access to your storage. You can create EBS General Purpose (SSD) and Provisioned IOPS (SSD) volumes up to 16 TB in size, and slower, legacy magnetic volumes.
Rackspace Cloud Block Storage: Rackspace

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