What is Cold Storage?

Cold storage is a data storage tier designed for information that is rarely accessed but must be retained for long periods, often years or decades. It prioritizes minimal cost per gigabyte over fast access speeds, making it suitable for backups, archival records, regulatory compliance data, and historical logs. Providers like Amazon S3 Glacier (introduced in 2012) and Azure Archive Storage (launched in 2017) exemplify this tier, with retrieval times measured in minutes (e.g., 1 to 5 minutes for Glacier Expedited) or hours (e.g., 12 hours for Azure Archive default).

Data written to cold storage is typically stored on high-density, low-power media such as magnetic tape or slow-spinning hard disk drives. To keep costs low, the provider may use erasure coding or replication across geographically separate facilities, but with limited redundancy compared to hot tiers. Retrieval requests are queued and processed asynchronously, and users often pay a per-GB retrieval fee in addition to the storage cost. Some services offer multiple retrieval speeds at different price points, such as Glacier's Expedited, Standard, and Bulk tiers.

Cold storage fits into the broader storage hierarchy as the deepest, cheapest layer, below hot (frequent access) and warm (infrequent access) tiers. It is commonly used in hybrid cloud architectures where on-premises data is backed up to the cloud for disaster recovery, or in media archives where old footage or documents must be kept for legal reasons. The tradeoff is clear: you save money on storage but accept slower access and higher retrieval costs, so it is not suitable for data that needs to be restored quickly or frequently.