What is Block Storage, and when do you need it
Quick answer
Block Storage gives you raw, networked disk volumes over iSCSI or Fibre Channel, with no filesystem attached. You format and manage the volume yourself, exactly like a local disk. Use it for VM disks and databases that need fast, low-latency random access. If you just need somewhere to write files once and read them back over HTTP, Object Storage is the simpler fit.
What it is
Block Storage presents your server or virtual machine with a volume made of raw, addressable blocks, comparable to a new local disk that happens to be accessible over a network. Nothing is imposed on top of it: no filesystem, no file hierarchy, no built-in access protocol beyond the block-level connection itself. You partition and format the volume the same way you would a physical disk, using whatever filesystem your operating system expects.
That directness is the point. Because each block is individually addressable, the storage layer doesn't need to interpret files or folders, so reads and writes go straight to the block, which is what gives Block Storage its low-latency, high-throughput profile.
How you connect to it
Block Storage volumes are attached over iSCSI or Fibre Channel, the standard protocols for presenting a networked disk to a server as if it were locally attached. Software-defined variants of these protocols are increasingly common too. Once attached, the volume behaves like local disk from the operating system's point of view: you can resize it, snapshot it at the OS or hypervisor level, and move it between hosts, but you're always working with a raw device, not a shared network folder.
When to use it
Block Storage suits workloads that need direct, low-latency access to a disk and manage their own data structures rather than relying on a shared filesystem:
- VM disks: the underlying storage for virtual machines, where the hypervisor needs fast, predictable block access.
- Production databases with high I/O, where query performance depends on consistent read and write latency.
- Big data and intensive analysis workloads that read and write large volumes of data continuously.
- Mission-critical, business-critical applications that need continuous availability and frequent data access.
In short: reach for Block Storage when the workload needs a filesystem it controls itself and cares about latency, not when it just needs to store and serve files.
Block Storage vs. Object Storage
These two get confused because both sit under "cloud storage," but they solve different problems. Object Storage is S3-compatible bucket storage: you write a file once through an HTTP API and read it back later, with no filesystem involved at all. Block Storage is the opposite in that respect: it is a filesystem's foundation, just one you manage yourself, and it's built for low-latency random access rather than write-once, read-many access over HTTP.
| Block Storage | Object Storage | |
|---|---|---|
| Access | iSCSI / Fibre Channel, attached like a local disk | S3-compatible HTTP API |
| Filesystem | None included, you format it yourself | None, objects in buckets |
| Best for | VM disks, databases, high-IO workloads | Backups, static assets, media, archives |
| Typical access pattern | Frequent random reads and writes | Write once, read many times |
If you're unsure which of the three storage products fits a given workload, including File Storage as a third option, see the full comparison linked below.
Sizing and pricing: Volume size limits, IOPS and throughput figures, and pricing are not listed here, because they change independently of this article. For current figures, see the Block Storage page on worldstream.com or open a support ticket in Portal before you size a specific workload.