By Graham Joys

As video surveillance systems expand to cover more cameras, higher resolutions, and longer retention periods, the reliability of storage infrastructure is more critical than ever. One of the most underrated threats is the Unrecoverable Read Error (URE), which can silently corrupt or destroy archived footage. While RAID arrays remain a mainstay for active surveillance data, LTO tape offers a robust solution-not only avoiding UREs entirely but also enabling video storage for much longer periods than disk-based systems.

What Are Unrecoverable Read Errors?

A URE occurs when a hard drive is unable to read a sector of data, even after multiple retries. These errors can be caused by physical media defects, firmware issues, or environmental factors. For consumer-grade drives, the typical URE rate is 1 in 10^14 bits read (about 12.5 TB), while enterprise drives may achieve 1 in 10^15 bits (about 125 TB). While these rates sound low, the sheer volume of data processed in modern surveillance systems means UREs are not just possible-they are statistically inevitable.

Why Are UREs a Problem for Video Surveillance?

Video surveillance data is typically written once and read infrequently, often only during investigations or compliance audits. This “write-once, read-rarely” pattern means that errors can remain hidden until a drive fails and a rebuild is required. During a RAID rebuild, every sector of every drive must be read to reconstruct lost data. If a URE is encountered during this process, the rebuild can fail, potentially resulting in the loss of days, weeks, or even months of footage.

RAID Configuration: Best Practices for Large Arrays

With the rise of high-capacity drives (28 TB and beyond), traditional RAID 5 configurations are no longer safe for large surveillance arrays. The risk of encountering a URE during a rebuild increases dramatically as drive sizes grow. For example, a single RAID 5 group of 24 × 28 TB drives is a ticking time bomb-failure during rebuild is almost guaranteed.

Key Recommendations:

• Split Large Arrays: Divide large storage pools into multiple smaller RAID groups (6–8 drives per RAID 5 group, or 8–12 drives per RAID 6 group).
• Use RAID 6 or RAID 60: RAID 6 offers dual-parity protection, reducing the risk of rebuild failure. RAID 60 (striped RAID 6 groups) further improves resilience and performance.
• Monitor and Scrub: Schedule regular RAID scrubs to detect and correct errors before they become critical.

Tiered Storage: The Superior Longevity and Reliability of LTO Tape

For long-term retention, LTO tape is not just an alternative-it’s a superior choice. Unlike RAID arrays, LTO tape is not susceptible to UREs, as its error correction and offline nature prevent the silent corruption that plagues disk-based systems. But the advantages go even further: LTO tape allows video storage for much longer periods-up to 30 years-when stored under proper environmental conditions (typically 18°C and 40% relative humidity)579.

Why Choose LTO for Surveillance Archives?

• No UREs: LTO’s offline, magnetic format means it’s not vulnerable to the UREs that can derail RAID rebuilds.
• Extended Lifespan: LTO tapes can reliably store data for 15–30 years, far exceeding the 3–5 year lifespan of hard drives or RAID systems567.
• Cost-Effective: LTO offers a lower cost per TB, especially for large archives, and uses less power than disk-based storage68.
• Security: Offline storage protects against ransomware, malware, and accidental deletion68.

When to Use LTO:

• Active Data: Keep recent footage (30–60 days) on RAID for fast access.
• Archives: Migrate older footage to LTO for cost-effective, long-term storage.
• Large Arrays: For total storage needs exceeding 500 TB, a hybrid RAID/LTO approach is recommended to balance performance, cost, and reliability.

Case Study: Citywide Surveillance

A city deploying 24 × 28 TB drives (672 TB raw storage) with a 90-day retention policy can reduce URE risk by splitting the array into two RAID 6 groups of 12 drives each (RAID 60). Recent footage is stored on RAID for quick retrieval, while older data is archived to LTO. This approach not only lowers the risk of data loss but also reduces operational costs and power consumption-and ensures video evidence is preserved for decades, not just years.

Best Practices for LTO Storage

To maximize the lifespan and reliability of LTO tapes:

• Store in a controlled environment: Maintain temperature and humidity within recommended ranges (ideally 18°C and 40% relative humidity)510.
• Keep tapes clean and dust-free: Store cartridges in protective cases and avoid exposure to contaminants10.
• Rotate and test tapes: Periodically check archived tapes for readability and migrate data as needed to avoid obsolescence9.

Unrecoverable Read Errors are a silent but serious threat to the integrity of video surveillance storage. By adopting best practices in RAID configuration, implementing regular monitoring, and integrating LTO tape for long-term archives, organizations can safeguard their footage and ensure compliance with regulatory requirements. LTO not only avoids UREs entirely but also enables video storage for much longer periods-making it an essential component of any modern surveillance storage strategy.

About The Author:
Graham Joys is founder and President of ViSTA Networking Solutions a video security provider of innovative surveillance and LPR solutions, dedicated to delivering high-quality products and services to meet the evolving needs of systems integrators.

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Source: vnssystems.com