Redundancy protects against a drive dying tomorrow. It does not protect against a file that flipped a bit six months ago and got rewritten to every copy in the pool before anyone noticed. Silent data corruption, sometimes called bitrot, is the quiet failure mode that RAID and mirrored volumes were never designed to catch, which is why every serious NAS setup layers a scrubbing schedule and a checksumming filesystem underneath the storage.
We looked at eight desktop apps and filesystem tools that a homelab or a small-office NAS actually runs to keep integrity checks on a schedule. Some are full operating systems that ship with scrub as a scheduled task, some are user-space tools that add parity to an existing directory, and one is a GUI wrapper for a filesystem that already checksums everything.
What to look for in a data integrity tool
The features that matter here are not the ones a marketing page leads with:
- Block-level checksums. The filesystem writes a hash for every block and compares it on read. Without this, corruption is invisible.
- Scheduled scrubs. A weekly or monthly job that walks every block and verifies its checksum. Manual scrubs get forgotten.
- Auto-repair. When the checksum mismatch is caught on a mirrored or parity volume, the tool rewrites the good copy over the bad one.
- Email or webhook alerts. A silent scrub that finds a problem and reports it only in a log file is a scrub that will surprise you.
- Snapshots. Point-in-time views that let you roll back if corruption is caught before it propagates.
- Cross-filesystem support. Not everyone can rebuild a pool. Tools that add parity or hashing to an existing ext4 or NTFS volume matter for existing setups.
Quick comparison
| App | Filesystem | Auto-repair | Scheduled scrub | Free plan |
|---|---|---|---|---|
| TrueNAS Scale | OpenZFS | Yes | Yes (GUI) | Full app, free |
| OpenZFS | OpenZFS | Yes | Yes (cron) | Free, open source |
| Btrfs | Btrfs | Mirror only | Yes (systemd) | Free, kernel-included |
| SnapRAID | Any (adds parity) | Yes (from parity) | Yes (scripted) | Free, open source |
| Restic | Any (backup) | No (verify only) | Yes (scripted) | Free, open source |
| Duplicati | Any (backup) | No (verify only) | Yes (GUI) | Free, open source |
| Unraid | XFS with parity | Yes (from parity) | Yes (GUI) | Paid license |
| Btrfs Assistant | Btrfs | Mirror only | Yes (GUI) | Free, open source |
1. TrueNAS Scale — Best for a full NAS OS with scrub built in
TrueNAS Scale is the OpenZFS-based NAS OS most people mean when they say “scrub the pool.” The web UI has a scheduled task for scrub, alerts by email or webhook, and one-click resilver on drive replacement. Because ZFS checksums every block, a scrub is what turns silent corruption into a reported and repaired event.
Where it falls short: rebuilding a pool to switch from Btrfs or ext4 to ZFS means moving the data off and back. Not a light change.
Pricing:
- Free and open source.
- Optional TrueNAS Enterprise for paid support.
Download: truenas.com/download-truenas-scale
Bottom line: the default answer for a new NAS build where the drives are yours to arrange.
2. OpenZFS — Best for adding ZFS to an existing Linux server
OpenZFS is the filesystem underneath TrueNAS, and it runs on any Linux distribution that can load the kernel module. Managing scrub is a zpool scrub tank cron job, and status shows up in zpool status. Every block carries a SHA-256 or Fletcher checksum, so a scrub finds and repairs corruption automatically when a redundant copy exists.
Where it falls short: no GUI in the base install. Command-line comfort is required.
Pricing:
- Free and open source under CDDL.
Download: openzfs.org
Bottom line: the right layer if a Linux server already exists and adding a ZFS pool is easier than migrating to a NAS OS.
3. Btrfs — Best for a kernel-included checksumming filesystem
Btrfs ships in every mainline Linux kernel and does the same job as ZFS on a smaller feature set. Enable checksumming (the default), schedule btrfs scrub start /mnt/pool as a systemd timer, and the filesystem walks every block on the schedule and reports mismatches. On mirrored or RAID1 volumes, it repairs from the good copy.
Where it falls short: RAID5 and RAID6 are still not recommended for production. Stick to single, mirror, or RAID10 profiles.
Pricing:
- Free and included in the Linux kernel.
Download: btrfs.readthedocs.io
Bottom line: for Linux users who want checksumming without leaving the kernel or installing a third-party module.
4. SnapRAID — Best for parity over an existing mixed-drive array
SnapRAID is the tool that made JBOD homelabs viable. It sits on top of any filesystem (ext4, XFS, NTFS, Btrfs) and computes parity across a set of data drives to a set of parity drives. snapraid sync writes the parity, snapraid scrub walks the array and verifies hashes, and snapraid fix restores corrupted files from parity.
Where it falls short: parity is only as fresh as the last sync. Files changed after the last sync are not protected until the next run.
Pricing:
- Free and open source under a GPL license.
Download: snapraid.it
Bottom line: the go-to add-on when the drives are different sizes and swapping filesystems is not an option.
5. Restic — Best for verified backups over any storage
Restic is a backup tool with a scrub-equivalent built in: restic check --read-data walks every pack in the repository, verifies the checksum, and reports mismatches. It backs up to local disks, SFTP, S3, Backblaze B2, and Rest Server, and every backup is deduplicated and content-addressed.
Where it falls short: it verifies backups, not the source data. Corruption on the primary volume still needs a filesystem tool to catch.
Pricing:
- Free and open source under BSD-2.
Download: restic.net
Bottom line: pair it with a checksumming filesystem for a two-layer defence: filesystem for live data, restic for the backup copy.
6. Duplicati — Best for a GUI-driven verified backup
Duplicati covers the same ground as Restic with a web UI, a scheduler, and support for a wider range of remote destinations including Google Drive, OneDrive, and Dropbox. The test-connection and verify-remote features run integrity checks on the encrypted archive after every backup.
Where it falls short: the query engine can be slow on very large repositories.
Pricing:
- Free and open source under LGPL.
Download: duplicati.com
Bottom line: the right pick for people who want a scheduled verified backup with a GUI, no scripts.
7. Unraid — Best for a paid NAS OS with parity and Docker
Unraid is the commercial NAS OS that took the SnapRAID approach and wrapped it in a polished web UI, a plugin ecosystem, and first-class Docker and VM support. Parity is calculated on write, monthly parity checks scrub the array, and the alerts panel surfaces bit errors before they matter.
Where it falls short: paid license per server. Not open source.
Pricing:
- Basic, Plus, and Pro license tiers, one-time purchase with lifetime updates on legacy licenses. Recent versions moved to an annual renewal for updates.
Download: unraid.net
Bottom line: for people who want the mixed-drive parity of SnapRAID without stitching together the tooling themselves.
8. Btrfs Assistant — Best for a GUI on top of Btrfs scrub
Btrfs Assistant is the Qt front-end for Btrfs administration that turns scrub scheduling, snapshot management, and balance operations into checkboxes. It exposes the same tools that ship with the kernel, so nothing under the hood changes, and it makes the “did I schedule a monthly scrub” question a one-click check.
Where it falls short: Linux only, and the layout is dense for first-time Btrfs users.
Pricing:
- Free and open source under a GPL license.
Download: github.com/btrfs-assistant/btrfs-assistant
Bottom line: install it on a Btrfs system that runs Plasma or GNOME, and stop editing crontabs.
How to pick the right one
For a fresh NAS build, install TrueNAS Scale and let the GUI handle the scrub schedule. For a Linux server that already exists, add ZFS with OpenZFS if the drives are matched, or SnapRAID if they are not. For a homelab that runs Docker and wants the polished commercial experience, Unraid is the paid path. If the filesystem stays put but the backups need verification, Restic or Duplicati adds the check. Btrfs Assistant covers the case where the pool is already Btrfs and the missing piece is a friendlier scheduler.
FAQ
What is the best free NAS integrity tool?
TrueNAS Scale for a full OS, OpenZFS or Btrfs to add checksumming to an existing Linux server, and SnapRAID when the drives are mismatched and moving data around is not an option.
How often should I scrub my NAS?
A weekly scrub is common for consumer drives, monthly for enterprise-grade disks. TrueNAS defaults to monthly with a threshold that skips if the previous scrub is recent enough.
Does RAID protect against silent data corruption?
Traditional RAID does not. It protects against a whole-drive failure but has no way to know which mirror copy is correct if the two disagree. Checksumming filesystems (ZFS, Btrfs) close that gap.
What is the difference between a scrub and a resilver?
A scrub reads every block and verifies its checksum. A resilver rebuilds a replaced disk from the other copies. Both find corruption, but only scrub is a scheduled maintenance operation.
Can I add integrity checks to an existing NTFS or ext4 volume?
Yes, with SnapRAID for parity, or Restic and Duplicati for content-hashed backups. The volume itself will not gain block-level checksums without moving to Btrfs or ZFS.