UK-Based Technical Service

Diagnosing and Repairing
Corrupted Backup Files

When a backup archive fails to open, reports CRC errors, or produces incomplete data on extraction, the underlying cause is rarely simple. We carry out structured file-level analysis to determine whether recovery is feasible and what can realistically be retrieved.

Describe Your Issue How It Works

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backup-diagnostic.sh

$ analyse-backup site_backup_2024.zip [INFO] Loading archive: site_backup_2024.zip [INFO] File size: 847.2 MB [WARN] Central directory offset mismatch [INFO] Scanning local file headers… [INFO] Found 1,847 entries in local headers [ERR] CRC mismatch on entry: wp-content/uploads/ [INFO] Attempting raw block extraction… [OK] Recovered 1,692 / 1,847 entries [WARN] 155 entries require manual inspection [INFO] Database dump: intact (SQL header verified) [OK] Report written to: recovery-report.txt $

Interactive Tool

Quick Backup Health Check

Answer four short questions about your backup file to receive a general diagnostic assessment. This is a preliminary indicator — not a substitute for professional inspection.

1 What format is your backup file?

2 What error or symptom are you seeing?

3 How large is the backup file?

4 Where was the backup created?

14 years of backup
diagnostics

Technical Background

How Backup Corruption Occurs

Backup files fail for a surprisingly wide range of reasons. Understanding the mechanism helps set realistic expectations about what recovery can achieve.

Interrupted Write Operations

If a backup process is terminated mid-run — due to a server timeout, power interruption, or process kill — the resulting file will be structurally incomplete. The header may appear valid while internal blocks are missing.

Storage Media Degradation

Magnetic and flash storage degrades over time. Bit rot — the gradual, silent corruption of stored data — can alter individual bytes within an archive without any visible warning until the file is next accessed.

Transfer Errors

Moving backup files over unreliable network connections — particularly via FTP without checksums — introduces the risk of dropped packets and misaligned data blocks. The file arrives intact in size but with altered content.

Compression Algorithm Failures

Multi-volume compressed archives and split ZIP files are particularly vulnerable. A missing volume segment or a corruption in one volume can prevent access to all subsequent volumes, even if they are individually intact.

Software and Plugin Errors

Backup software can produce malformed archives when encountering unexpected file types, overly long paths, or files that change during the backup window. Some WordPress backup plugins are known to produce partial SQL dumps under load.

Cloud Storage Export Issues

Cloud-exported backups occasionally arrive with incorrect file sizes or truncated streams, particularly when downloaded from object storage over slow or interrupted connections. This is a common and underappreciated cause of archive damage.

Read the Full Article on Corruption Causes

What We Work On

Recovery & Repair Services

Each service is tailored to the specific structure and failure modes of the backup format involved. There is no single-tool approach to backup recovery.

Archive Recovery

Backup Archive Repair

Structural analysis and partial or full recovery of damaged ZIP, TAR, GZ, 7Z and similar archive formats. Covers both single-volume and multi-part archive sets.

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Available

Database Recovery

Database Backup Repair

Inspection and repair of SQL dump files, MySQL and PostgreSQL backups, and damaged binary database export files. Focused on schema and data integrity verification.

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Available

WordPress Recovery

WordPress Backup Repair

Recovery from corrupted WordPress backup packages including those generated by UpdraftPlus, BackupBuddy, Duplicator, and manual archive exports.

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Available

Methodology

The Repair Process

Recovery work follows a consistent diagnostic pathway. Each stage informs whether it is viable to proceed to the next.

File Inspection

Raw byte-level examination of the file structure. Header signatures, magic bytes, and metadata offsets are verified against the format specification.

Structure Analysis

Mapping of the archive's internal directory structure. Identifying which entries are intact, partially damaged, or completely unreadable.

Repair Attempt

Where feasible, targeted reconstruction of damaged sections. This may include header repair, offset correction, or extraction of intact blocks from a fragmented stream.

Verification

All recovered data is verified against available checksums. SQL dumps are parsed for structural integrity. File counts and sizes are reconciled against backup manifests where available.

Reporting

A written report detailing what was found, what was recovered, what could not be recovered, and any recommendations for preventing recurrence.

Self-Assessment

Is Your Backup Strategy Sound?

Check the practices you currently follow. This assessment will score your current backup posture based on widely-accepted best practices. It is not exhaustive, but it highlights common gaps.

Regular backup frequency: Backups run at least once daily for critical systems.

Verified restores: You periodically test restoring from a backup rather than assuming the process works.

Off-site storage: At least one backup copy is stored in a separate physical location or cloud provider.

Multiple retention points: You keep more than one version, not just the most recent backup.

Checksum verification: Your backup tool records checksums and verifies them after each backup run.

Backup monitoring: You receive alerts when a scheduled backup fails or produces an unexpected result.

Database consistency: Database backups are taken with the service in a consistent state (e.g., using mysqldump --single-transaction).

Documented procedure: A written recovery procedure exists and has been reviewed in the last 12 months.

Select the practices you currently follow above.

Note on this assessment: The questions above reflect common recommendations from infrastructure best-practice guidelines. Scoring well on this assessment does not eliminate the risk of backup failure, but it does reduce the frequency and severity of incidents.

Read Our Technical Articles

The Team

Technical Staff

Our team consists of technicians with backgrounds in systems administration, file format analysis, and database engineering.

James Hartwell

Lead Diagnostician

Fourteen years working with archive formats and database recovery. Began in server administration before moving into specialised file analysis work.

Rachel Osei

Database Recovery Specialist

Focused on MySQL, PostgreSQL, and MariaDB backup analysis. Has experience recovering large-scale e-commerce database dumps from partial SQL exports.

Daniel Marsh

WordPress Recovery Lead

Specialises in WordPress and CMS platform backup structures. Works primarily with plugin-generated archives and hosting panel export files.

Priya Nair

Archive Format Analyst

Background in binary file format analysis and low-level data extraction. Handles cases involving rare or proprietary archive formats and multi-volume splits.

Client Feedback

What Clients Have Said

These are brief summaries of client experiences. Recovery outcomes vary depending on the nature and extent of the damage involved.

We had a 3.2GB WordPress archive from a site migration that simply wouldn't extract. The team provided a clear written assessment within two days and managed to recover the database and most of the uploads folder. The media library was mostly intact, which was the critical part for us.

Mark R. E-commerce business owner, Bristol

The SQL dump from our hosting provider was truncated — it cut off in the middle of an INSERT statement. I had assumed the data was gone. The recovery service identified the cut point and was able to reconstruct approximately 90% of the records. Not perfect, but far better than starting over.

Sarah K. Software developer, Manchester

I appreciated the transparency in the initial assessment — they told us upfront what was likely recoverable and what probably wasn't, rather than overpromising. The final result aligned with what they had described. That kind of honesty is not always easy to find with technical services.

Thomas G. IT manager, financial services firm, London

We had a server snapshot archive from a cloud export that was showing CRC errors on extraction. The team identified that only a small section of the archive was affected and extracted around 95% of the content without needing to touch the damaged block. Extremely useful turnaround.

Anya W. Systems administrator, Edinburgh

What struck me was the level of technical detail in their report. It wasn't just a summary of what they did — it explained exactly where the corruption was in the file structure, why it had likely happened, and what steps we should take going forward. Worth having for the documentation alone.

James L. Infrastructure consultant, Birmingham

I sent over a multi-part ZIP archive where two of the volumes were missing. I had low expectations, but they were able to extract the entries that were contained entirely within the remaining volumes. A sensible and realistic approach to a genuinely difficult problem.

Caroline F. Freelance web developer, Leeds

Technical Reading

Insights & Articles

Practical and educational articles on backup systems, corruption patterns, and recovery methodology.

Backup Integrity 9 min read

Diagnosing and Repairing
Corrupted Backup Files

Quick Backup Health Check

How Backup Corruption Occurs