<metaname="description"content="A backup program for disk arrays. It stores parity information of your data and it recovers from up to six disk failures">
<metaname="keywords"content="snapraid snapshot raid backup disk array redundancy parity">
<strongstyle="color: var(--text-primary);">SnapRAID</strong> is one of many <strongstyle="color: var(--text-primary);">RAID-like</strong> solutions available for disk arrays.
- A commercial solution (only the RAID core is GPL2). It uses a modified Linux XFS filesystem with real-time redundancy. Integrity checksums are not natively supported.
- <strongstyle="color: var(--danger); font-size: 0.75rem; border: 1px solid var(--danger); padding: 1px 4px; border-radius: 4px; vertical-align: middle;">DISCONTINUED</strong>. A commercial, proprietary C++/Java application for Windows, with limited Linux support. It offered both snapshot and real-time redundancy, including integrity checksums.
- An open-source (GPL2) Linux filesystem with real-time redundancy. Since Linux 3.9, it supports <ahref="http://lwn.net/Articles/536038/"target="_blank"rel="noopener">RAID5/6 redundancy</a> and integrity checksums.
Issues have been identified, and the official <ahref="https://btrfs.readthedocs.io/en/latest/btrfs-man5.html#raid56-status-and-recommended-practices"target="_blank"rel="noopener">wiki</a> as of 2026 warns:
<emstyle="display: block; margin-top: 0.5rem; color: var(--text-secondary); background: rgba(255,255,255,0.03); padding: 0.5rem; border-radius: 4px;">"There are some implementation and design deficiencies that make it unreliable for some corner cases and the feature should not be used in production, only for evaluation or testing."</em>
- Microsoft’s solution, integrated into Windows 8 and later. Proprietary, with real-time redundancy but no checksum support. It also has several <ahref="https://helgeklein.com/blog/windows-8-storage-spaces-bugs-and-design-flaws/"target="_blank"rel="noopener">limitations</a>.
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<h2>Key Takeaways</h2>
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<h3>Real-time vs Snapshot</h3>
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The primary factor for categorizing storage solutions is when redundancy information is updated. This timing determines whether the system acts as a live mirror or a point-in-time recovery tool.
In <strongstyle="color: var(--text-primary);">real-time</strong> solutions, parity is updated immediately during every write operation without user action. While this ensures the array is constantly protected against hardware failure, it does not allow for the restoration of an earlier state, meaning accidental deletions are propagated instantly.
In <strongstyle="color: var(--text-primary);">snapshot</strong> solutions, parity is updated only upon an explicit request, similar to a backup. This creates a fixed point in time that allows to recover files that were accidentally deleted or modified since the last sync.
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<h3>Integrity & Bitrot</h3>
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Silent data corruption, or bitrot, is a <ahref="https://www.zdnet.com/article/data-corruption-is-worse-than-you-know/"target="_blank"rel="noopener">major threat</a> where storage devices return corrupted data without reporting hardware errors. Unlike traditional disk failures, this bit-level degradation remains invisible until the data is accessed or an array reconstruction is attempted.
A primary factor in categorizing storage solutions is their support for <strongstyle="color: var(--text-primary);">integrity checksums</strong> to detect and repair this corruption. Advanced systems use hashing to verify data blocks, allowing them to identify silent changes even if timestamps remain unaltered and use parity data to reconstruct the original, uncorrupted information.
unRAID can use integrity checksums via plugins like <ahref="https://forums.lime-technology.com/topic/43290-dynamix-file-integrity-plugin/">Dynamix File Integrity</a> or <ahref="https://forums.lime-technology.com/topic/35615-bunker-yet-another-utility-for-file-integrity-checks/">bunker</a>. However, these are independent of parity processing and not used to aid recovery. For example, when recovering a single failed disk with dual parity, checksums can identify additional silent errors to facilitate recovery. To achieve functionality similar to SnapRAID, you would need to use the Btrfs filesystem for all your data disks.
Storage Spaces can be used with ReFS, which supports integrity checksums, but not in Parity mode: <ahref="http://www.windowscentral.com/how-use-resilient-file-system-refs-windows-10"><i>"Although you may select Simple (no resiliency) or Parity, both options will fail the process."</i></a>
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Fix Silent Errors
<divclass="cell-subtext">Whether silent errors are detected and fixed before propagating to parity.</div>
unRAID lacks native checksums and ignores silent errors. Even worse, if a parity mismatch is detected due to a silent error in the data, the parity is automatically recomputed, making it impossible to recover the silent error, even manually. Integrity checksum plugins do not help in this case, as they are not integrated into the parity-checking process.
ZFS provides bit-rot protection comparable to SnapRAID. One drawback of ZFS is that its default Fletcher checksum prioritizes speed over reliability. SnapRAID uses 128-bit SpookyHash.
unRAID 7.2 claims it can add data disks to an existing array, but it effectively rebuilds parity from scratch. During this process, disks already in the array <ahref="https://youtu.be/frtauLMO3-c?t=803">are not protected</a>. This puts stress on all drives with no safety net. If any disk is near failure, there’s a high risk it could fail during this operation. With unRAID, the only safe way to add a new data disk to an existing array is to pre-clear it first.
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<tdclass="cross">No</td>
<tdclass="cross">No</td>
<tdclass="cross">No</td>
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<tdclass="feature-cell">Operating System
<divclass="cell-subtext">Which operating systems are supported?</div>
Btrfs has supported RAID5 since 2013, but serious issues in RAID5/6 support were <ahref="https://www.phoronix.com/scan.php?page=news_item&px=Btrfs-RAID-56-Is-Bad">identified</a>. As of 2026, these remain unresolved. The official <ahref="https://btrfs.readthedocs.io/en/latest/btrfs-man5.html#raid56-status-and-recommended-practices"target="_blank"rel="noopener">wiki</a> states that RAID5/6 support should not be used in production.
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<td>2012</td>
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<tdclass="feature-cell">License / Price
<divclass="cell-subtext">Software license and cost.</div>
