Understanding Block, File, and Object Storage: Pros, Cons, and Use Cases

Block Storage

Typical devices: disk arrays, hard drives. Block storage maps raw disk space directly to hosts, often using RAID, LVM, or logical partitions. The OS sees the logical disks as separate physical disks, requiring partitioning and formatting before use, just like local disks.

Advantages

Data protection through RAID/LVM.

Combine multiple inexpensive disks into a large logical volume.

Parallel writes improve read/write efficiency.

SAN architecture can boost transfer speed and protocol efficiency.

Disadvantages

Requires additional hardware such as Fibre Channel cards and switches, increasing cost.

Data cannot be shared between hosts without clustering; each host treats the mapped disk as local.

Different OS file systems (e.g., NTFS vs EXT4) cannot share data directly.

File Storage

Typical devices: FTP, NFS servers. File storage enables easy file sharing without the need for host-side formatting because the storage system handles file management. A regular PC with appropriate OS and software can act as a file storage server.

Advantages

Low cost: can run on ordinary hardware using standard Ethernet.

Convenient file sharing.

Disadvantages

Lower read/write speed due to Ethernet limitations and reliance on a single server's disks.

Object Storage

Typical devices: distributed servers with large-capacity disks running object‑storage software and dedicated management nodes. Object storage combines the speed of block storage with the sharing capability of file storage.

Each object consists of metadata (size, modification time, path, etc.) and data. Metadata is stored separately on a metadata server, while the actual data resides on multiple Object Storage Devices (OSDs). When a client requests an object, the metadata server tells which OSDs hold the data, allowing parallel data retrieval and higher throughput.

Object storage also provides its own file system, eliminating sharing difficulties and supporting large‑scale data distribution.

Key Technologies

Distributed metadata.

Concurrent data access via OSDs.

What is an OSD?

OSD (Object Storage Device) manages object data, stores it on standard disks, and handles read/write operations using object IDs and offsets. It also performs intelligent data placement, prefetching, and metadata management.

Below is a brief diagram summarizing the differences among block, file, and object storage:

Why use block or file storage when object storage already combines their benefits?

Some applications (e.g., databases) require raw disk mapping and formatting, making block storage more suitable.

Object storage incurs higher costs due to specialized software and large disks; for modest data volumes, file storage may be more cost‑effective.