RAID

What is RAID?

RAID (Redundant Array of Independent Disks) combines multiple drives into one storage arrangement. Depending on the RAID level, it may use striping for performance, mirroring for redundancy, or parity to help recover data after a drive failure.

RAID is redundancy, not a backup. It does not protect against accidental deletion, malware, theft, fire, or every type of hardware and software failure.

Why does RAID matter when buying or comparing?

RAID support can affect:

• Drive requirements: Different RAID levels require different numbers of drives.
• Usable capacity: Some capacity may be used for mirrors or parity rather than storing files.
• Failure protection: RAID levels provide different types and amounts of redundancy.
• Performance: The way data is distributed can affect read and write behavior.
• Maintenance: Online expansion, online migration, and rebuild support can affect how changes and drive failures are handled.

Product listings may show levels such as RAID 0, 1, 5, 6, 10, 50, and 60. They may also list JBOD or variants such as +HS or +S; these labels should be checked against the manufacturer’s documentation.

When does RAID matter, and when does it not?

RAID matters when a product will use multiple drives and continued access to data after a drive failure is important. It is especially relevant for NAS devices, servers, and storage systems that hold shared or otherwise important files.

It matters less when the product uses one drive, when the data is temporary, or when a separate backup is the main protection requirement. RAID 0 provides striping without drive redundancy, while JBOD generally presents drives together without being a RAID protection level.

What does RAID NOT tell you?

A RAID support flag is not a quality rating. “RAID: Yes” does not show which levels are supported, how well they perform, or how reliable the implementation is.

RAID support also does not tell you:

• The number of drive bays or the required drive count
• The usable capacity after mirroring or parity
• The level of fault tolerance
• Rebuild duration or behavior
• Whether expansion or migration can be performed online
• Whether all RAID features work with every drive type or configuration
• Whether your data is backed up

A product with more listed RAID levels is not automatically better. The suitable level depends on your capacity, performance, availability, and recovery needs.

What should you check on a product page or spec sheet?

Check the exact details rather than relying only on a general RAID support flag:

1. Supported RAID levels: Confirm the levels you need, such as 0, 1, 5, 6, or 10.
2. Drive requirements: Check the minimum and maximum drive count and whether drives must meet particular requirements.
3. Usable capacity: Look for the capacity available after mirroring or parity.
4. Expansion and migration: Confirm whether online RAID expansion and online RAID migration are supported, and under what conditions.
5. Rebuild support: Check whether RAID rebuild is supported and review any documented restrictions or recovery process.
6. Hot-spare terminology: If the listing uses HS or S, verify what those abbreviations mean for that product.
7. Drive compatibility: Review the manufacturer’s compatibility information for drive types, capacities, and configurations.
8. Backup options: Confirm how the product can be backed up independently of RAID.

Observed product specifications on NASFit include separate flags for RAID support, online expansion, online migration, and rebuild support. These flags describe listed capabilities; they do not by themselves establish performance, reliability, or implementation quality.

Related terms worth understanding

• RAID 0: Striping without redundancy.
• RAID 1: Mirroring data across drives.
• RAID 5: Parity-based RAID commonly used with multiple drives.
• RAID 6: Parity-based RAID with a different redundancy arrangement from RAID 5.
• RAID 10: A combination of mirroring and striping.
• JBOD: A drive arrangement that is not, strictly speaking, a RAID protection level.
• Backup: A separate copy of data used for recovery; RAID does not replace it.