What is Secondary Storage? Types, Uses, and Why It Matters for Backup

1 July 2025 By BOBcloud Team BOBcloud

Primary vs Secondary Storage

To understand secondary storage, it helps to start with primary storage. Primary storage is where a computer or server stores the data it is actively working with — RAM (Random Access Memory) and, by extension, the data on fast local disks that applications read from and write to in real time. It is fast, expensive, and temporary.

Secondary storage is everything else. It is where data lives when it is not being actively processed — files, databases, archives, backups. Secondary storage is slower than primary storage, but it is far cheaper, has much higher capacity, and is persistent: data stays there when the power is off.

The distinction matters because backup strategy is fundamentally about moving data from primary storage (where it is at risk) to secondary storage (where it is protected).

Types of Secondary Storage

Hard Disk Drives (HDD)

Traditional spinning hard drives remain one of the most cost-effective forms of secondary storage for large volumes of data. They are slower than SSDs but significantly cheaper per gigabyte, making them well suited for backup repositories, NAS devices, and archival storage.

Solid State Drives (SSD)

SSDs use flash memory rather than spinning platters, making them significantly faster than HDDs. They are used as secondary storage where performance matters — for backup repositories that need to support fast restores, or as a staging area before data is moved to slower archival storage.

Network Attached Storage (NAS)

A NAS device is a dedicated storage appliance connected to a network, accessible by multiple devices simultaneously. NAS systems are widely used for on-premises backup storage, file sharing, and archival. They typically use HDDs and support RAID configurations for resilience.

Tape Storage

Tape is one of the oldest forms of secondary storage and remains in use for long-term archival and compliance retention. Modern tape formats (LTO-9 and later) offer very high capacity at low cost per gigabyte. Tape is offline storage — data on tape is not connected to any network, making it immune to ransomware and other network-based attacks.

Cloud Storage

Cloud storage has become the dominant secondary storage medium for backup in most organisations. Services like Azure Blob Storage, Amazon S3, and purpose-built cloud backup platforms offer effectively unlimited capacity, geographic redundancy, and access from anywhere. Cost per gigabyte is low and falling.

Cloud storage used for backup combines several desirable properties: offsite location (protecting against local disasters), network separation from on-premises infrastructure (important for ransomware resilience), and scalability without hardware investment.

Secondary Storage in Backup Architecture

Most modern backup architectures use a combination of secondary storage types, often following principles like the 3-2-1 rule:

  • 3 copies of data
  • 2 different media types
  • 1 copy offsite

A typical implementation: primary data on local servers (primary storage), backup to a local NAS (secondary storage, fast restore), and backup to cloud (secondary storage, offsite, disaster recovery).

The local copy provides fast recovery from day-to-day issues like accidental deletion. The cloud copy provides protection against local disasters — fire, flood, ransomware that compromises the local network.

Secondary Storage and Recovery Time

One of the key decisions in backup architecture is how to balance cost against recovery time. Secondary storage on slower, cheaper media means longer restore times. Secondary storage on faster, more expensive media means faster restores but higher cost.

For critical systems with low RTO (Recovery Time Objective) requirements, faster secondary storage — SSDs, high-performance NAS, or cloud storage with fast connectivity — is worth the cost. For less critical data with more generous RTOs, slower archival storage is appropriate.

For MSPs: Designing Secondary Storage for Client Backup

When designing backup architecture for clients, secondary storage decisions directly affect both cost and the ability to meet SLA commitments. Key questions to consider:

  • What is the client's RPO (how frequently must backups run)?
  • What is the client's RTO (how quickly must data be recoverable)?
  • What volume of data needs to be protected?
  • Is on-premises secondary storage available, or is cloud-only appropriate?
  • What are the compliance or retention requirements?

BOBcloud provides cloud secondary storage specifically optimised for MSP backup workloads, with per-GB pricing and no egress fees for restore. Find out more about our MSP backup platform.