Explain the difference between object, block, and file storage, and give one good use case for each.
What they are really testing: Whether you can match a storage type to a workload instead of defaulting to one for everything. They want the access model for each and a sensible use case, not just the product names.
A real interview question
Explain the difference between object, block, and file storage, and give one good use case for each.
What most people say
drag me
“Object is S3, block is a hard drive, file is for files. You mostly just use S3.”
It names products without the access model and defaults to one type for everything. The whole point is matching the access pattern (HTTP key lookup vs an attached volume vs a shared mount) to the workload, which this skips.
The follow-ups they ask next
Your team wants to run a relational database directly on object storage to save money. What do you tell them?
Object storage is not a mountable low-latency block device and you cannot edit objects in place, so a database needs block storage. Use object storage for the database backups instead.
Three app servers need to read and write the same uploaded files. Which type, and why not block?
File storage, because many instances can mount it simultaneously. A block volume normally attaches to a single instance, so it cannot be the shared read-write target for all three.
What the interviewer is listening for
- Describes the access model, not just product names
- Gives a fitting use case for each type
- Knows block is single-attach and file is shared-mount
What sinks the answer
- Defaults to one storage type for everything
- Suggests a database on object storage
- Cannot explain how each is accessed
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“Object storage is [accessed by key over HTTP, not mounted], good for [backups and static assets]. Block storage is [a volume attached to one instance], good for [a database or OS disk]. File storage is [a shared mount many instances use], good for [shared files across servers].”
Keep going with storage
Foundation
What is the difference between durability and availability for storage?
Foundation
What is the difference between backup and replication, and why is replication not a backup?
Junior
How does object storage achieve such high durability?
Junior
What consistency guarantees does object storage give, and why does it matter?
Junior
For block storage, what is the difference between IOPS and throughput, and how does it affect volume choice?
Mid
Design durable, highly available storage for user-uploaded images. Which service do you choose and why?
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