What is Block Storage?

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Block storage is a storage method where each volume functions like an independent hard drive, set up by the storage administrator. The data is saved in blocks of a fixed size. A unique address acts as metadata to describe each block. There is specific software, separate from the storage media, that manages how the blocks are allocated and arranged on the disk. The same software handles retrieval by using the addresses to locate the necessary blocks and reassemble them into the files requested by the user. Typically, the server operating system controls this block storage management software.

Access to block storage is provided through high-performance protocols like Fiber Channel over Ethernet (FCoE) or Internet Small Computer Systems Interface (iSCSI). It’s perfect for high-performance, mission-critical applications and can deliver high I/O performance with low latency. Block storage is often used in storage area network (SAN) environments as a high-performance option compared to file storage.

There are several cloud-based block storage services to choose from, including Azure Managed Disk, Google Cloud Persistent Disk, and AWS Elastic Block Storage. This is part of a series of guides on cloud storage.

Block Storage Pros and Cons

Block storage is commonly used in modern data centers because of its many advantages −

• Performance − Block storage is ideal for applications needing high IOPS and low latency, such as database servers.
• Flexibility − Organizations can grow storage by adding more block storage volumes without performance loss. Block storage can be transferred between servers by changing the destination path.
• File modification ease − When modifying a file in block storage, the system only needs to update the specific block affected. This differs from file or object storage, where the entire file or object must be overwritten.
• Bootable operating systems − Operating systems can boot directly from block storage through a SAN, assuming the server BIOS supports this feature.

However, block storage has some downsides, including −

• Server Binding − Block storage is tightly linked to the server, preventing access by other servers simultaneously. Certain software solutions address this issue, but they put more strain on the file system, which can lower performance.
• Metadata Limits − Block storage has limited metadata, much less than file or object storage. This can slow down operations like search and retrieval because the system can’t find data based on meaningful metadata and may need to search through many blocks to locate the necessary data.
• Cost − block storage is expensive. SANs require significant investment, and specialized personnel are needed for maintenance. Large organizations will notice block storage becoming a significant part of their cloud expenses.

Block Storage vs Object Storage

Object storage saves data as objects, which consist of three parts −

• File mapping − objects are not always mapped directly to files. They might represent parts of a file or related data that isn’t in a file.
• Metadata − the metadata can be created by the object library author. It includes information like content details, usage purpose, creation or modification dates, owners, permissions, and more.
• A unique identifier − the identifier is a 128-bit value unique to an object, allowing the object to be located in distributed storage. This lets object storage systems locate data without knowing its physical location (it could be in different areas of a data center or even spread across the globe).

Difference Between Block Storage and Object Storage

Object storage is much cheaper than block storage. Its scalability allows organizations to store vast amounts of data at low costs. Cloud services like Amazon S3, Azure Blob Storage, and Google Cloud Storage use object storage systems.

Object storage provides limitless metadata, making it highly customizable. Metadata can contain everything from security information to application-specific data. Large web platforms such as Facebook and Spotify rely on object storage for handling photos and media, while enterprise data centers use it for the same types of content, ensuring both high availability and reliability.

However, object storage doesn’t let users modify parts of a file. Objects are treated as whole units, meaning they can only be accessed, updated, or rewritten as a whole. This impacts performance when objects are large.

Also, operating systems can directly access block storage as if it were a local disk, but they can’t do the same for object storage, or if they can, it leads to performance degradation.

That said, object storage requires little to no ongoing management, unlike block storage, which involves continual maintenance and remapping.

File Storage vs Block Storage

File storage organizes data into a hierarchical system. Files are stored in the same structure as they were created. File storage uses protocols like Server Message Block (SMB) in Windows or Network File System (NFS) in Unix/Linux systems.

SMB and NFS allow files to be stored on a server, just like they would be on a local drive. Administrators can mount parts of the file system and share them with multiple client devices.

NAS devices are widely used for file storage sharing and can also offer backup options to ensure redundancy. These devices expand file storage beyond directly connected disks to network-attached storage.

Difference Between Block Storage and File Storage

The following table shows the differences between block storage and file storage −