DigitalOcean Spaces provide S3-compatible object storage which lets you store and serve large amounts of data. You can create them in a few seconds and use them immediately with no configuration. Data transfer is automatically secured with HTTPS, and the available storage capacity scales seamlessly.
Spaces are ideal for storing static, unstructured data like audio, video, and images as well as large amounts of text. Because Spaces are an object storage implementation, use cases like databases, applications written in server-side languages, and mission-critical applications will work best with local storage or block storage.
Refer to below link for more information on Spaces
Coming to Block Storage Volumes, it acts like a external HDD to your laptop.
Block storage volumes are network-based block devices that provide additional data storage for Droplets. You can move them between Droplets and resize them at any time. Refer to below for Volume features
For more insights on Volumes, please check https://www.digitalocean.com/docs/volumes/
Please check this article to better understand the differences between Spaces and Volumes https://www.digitalocean.com/community/tutorials/object-storage-vs-block-storage-services
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Flexible and scalable data storage is a baseline requirement for most applications and services being developed today. With today's complex deployments, containers, and ephemeral infrastructure, the days of simply saving files to disk on a single server are gone. Cloud providers have developed services to fill the storage needs of modern application deployments, and they mostly fit into two categories: object storage, and block storage.