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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesProtect an archive with layers: keep at least three copies on two different storage media, place copies in separate physical locations, create and retain checksums when files enter the archive, compare those checksums on a fixed schedule, and maintain a documented way to replace a damaged copy. A checksum can prove that bytes changed; it cannot rebuild the original file. You need an intact independent copy for repair.
What can go wrong in an archive?
Bit rot and silent corruption
Bit rot is an umbrella term for unintended changes to stored bits. A file may still open while a small section has changed, or an application may report an error only when it reaches the damaged portion. Silent corruption is especially dangerous because ordinary file browsing does not test every byte.
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Drive electronics, flash cells, controllers, cables, power events and filesystem errors can all contribute to corruption. The practical question is not which mechanism caused a change; it is whether the current file still matches a trusted earlier record.
Drive failure and loss
A failed drive can make an entire collection unavailable at once. Theft, fire, flooding, accidental deletion and ransomware can remove several devices in the same incident if they are kept together. Redundancy protects against one failure only when another copy is genuinely independent and reachable.
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Format and technology obsolescence
A bit-perfect file is not necessarily a usable file. An old codec, proprietary format, application, operating system or connector may disappear even though every byte remains intact. Integrity controls detect loss or alteration; format monitoring and planned migration preserve future access.
The minimum architecture: copies, media and locations
Use three copies across two media types
The Library of Congress’s digital-preservation guidance, updated December 27, 2023, states: “Save three copies of digital files on at least two different kinds of storage media made by different manufacturers.” Its personal-preservation guidance likewise recommends multiple media types in separate physical locations. Treat this as a design rule, not as a guarantee that any particular device will last.
A practical arrangement is:
- Working copy: the copy you normally use and update.
- Local recovery copy: a separate device used to restore quickly after a working-drive failure.
- Off-site copy: a copy kept in another building or geographic location, or maintained by a storage service in a separately managed environment.
Use at least two storage media categories, such as an external hard drive plus cloud storage. If all three copies are on identical drives in the same enclosure, one power event, theft or software mistake can affect all of them.
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Independence matters more than the label “backup”
A mirrored volume or redundant array can keep a system running when one member fails, but its members are usually in the same place and exposed to the same administrator, power event and malware. A mirror is useful operational redundancy; it is not a substitute for an independently stored backup. Keep at least one copy disconnected or otherwise protected from routine changes when your operating procedure permits, and keep another copy away from the primary site.
Build the archive at ingest
Establish the evidence needed for later checking before files circulate among devices. The following workflow creates a baseline and verifies each copy.
- Inventory the material. Record the source, date received, filenames, sizes, directory structure and any relevant creator or rights information. Decide which files are authoritative and which are temporary derivatives.
- Stabilize names and structure. Use a documented naming convention and preserve the original path or identifier in metadata. Do not silently overwrite a file that has the same name but a different revision.
- Calculate a cryptographic checksum for every file. Common choices include SHA-family hashes; MD5 is also described in preservation guidance for manifest comparisons. Record the algorithm, exact digest, file path, byte size, timestamp and the software or command that produced it.
- Create an aggregate manifest. Keep a machine-readable list of all file-level entries and a higher-level record for the collection, folder or package. The Library of Congress recommends establishing fixity as early as possible and logging it at both file and aggregate levels.
- Write the manifest outside the data set it describes. Store a copy with the archive, another with the recovery copy and another at the off-site location. A manifest stored only on the potentially damaged drive cannot serve as an independent baseline.
- Make each preservation copy. Copy the files to the local recovery medium and the off-site destination. Preserve directory structure and metadata where the destination supports it.
- Verify every destination by reading it back. Recalculate checksums on each new copy and compare them with the ingest manifest. Treat a failed comparison as an incomplete copy, not as a minor warning.
- Document access requirements. Note formats, codecs, fonts, software versions, hardware interfaces, encryption details and any license or key needed to open the files. This documentation addresses future usability rather than byte-level integrity.
How to check whether archived files have changed
Compare current checksums with the baseline
At each review, read the current file, calculate the same hash algorithm used at ingest and compare the result with the retained manifest. A matching digest is evidence that the tested bytes match the baseline; it is not proof that the file’s format will remain readable. A mismatch means the bytes differ, whether through corruption, an intentional edit, a mistaken replacement or a changed metadata wrapper.
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Use the same algorithm and path conventions consistently. If a preservation system normalizes line endings, recompresses files or changes embedded metadata, record that as a new version rather than treating the resulting digest as an unexplained failure.
Set a fixed interval and keep an audit trail
The National Digital Stewardship Alliance Levels of Digital Preservation (2013, Version 1) include checking fixity at fixed intervals, maintaining logs, detecting corrupt data and, at more advanced levels, replacing or repairing corrupted data. The document does not prescribe one universal consumer schedule. Choose an interval that reflects the archive’s importance, rate of change, media risk and ability to complete a full read, then put the date on a calendar or in an automated job.
For each run, log:
- the start and finish time;
- the device, account or storage location checked;
- the manifest version and hash algorithm;
- the number of files and bytes tested;
- matches, mismatches, unreadable files and missing paths;
- the person or process that ran the check;
- the action taken and the date it was completed.
Keep logs in more than one location and include them in your routine backup. A history of clean checks demonstrates continuity; it also helps identify when a problem first appeared.
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- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
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What to do when a checksum fails
- Stop editing the suspect copy. Preserve the mismatching file and its log entry so the condition can be investigated.
- Confirm the result. Re-read the file and recalculate its checksum. Check that the correct manifest version, path and algorithm were used.
- Compare other copies. Test the corresponding file on the local recovery and off-site copies. Do not assume the newest copy is correct; the manifest and corroborating copies are the reference.
- Quarantine the damaged version. Move it out of the active path or mark it read-only so it cannot overwrite a clean copy.
- Restore from an intact copy. Copy the verified file into the archive, preserve its metadata and recalculate its checksum after restoration.
- Record the repair. Link the replacement to the original incident, note which source was used and retain the old damaged file only if it is useful for investigation and does not create confusion.
- Escalate repeated failures. If a device produces multiple mismatches or read errors, remove it from preservation service and migrate its contents to a current medium. Test the replacement before returning it to the rotation.
Checksums detect a difference; they do not contain enough information to reconstruct missing or altered bytes. If every independent copy has the same damaged content, a checksum cannot repair the archive. Recovery then depends on another source, an earlier version or specialist data-recovery work, with no assurance that the original can be restored.
Refresh media before it becomes a crisis
Media life varies by device, usage, storage conditions and manufacturing batch. The Library of Congress personal-preservation FAQ says to migrate saved copies to a current storage medium about every five years. Another Library of Congress guide recommends replacing media every three to five years. These are planning recommendations, not a universal service-life statistic or a promise that a drive will fail on a particular date.
The National Archives advises copying content into a current storage environment as soon as possible for both solid-state and magnetic media because life expectancy differs. Use the earlier of a planned refresh date, warning signs, or a change in the surrounding technology.
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A safe migration sequence
- Acquire the destination medium and confirm it has enough capacity for the data, manifests, logs and expected growth.
- Run a fixity check on the source before migration. Resolve existing mismatches first.
- Copy the files and preservation metadata to the new medium.
- Read the destination back and compare every checksum with the pre-migration manifest.
- Make or update the independent off-site copy before retiring the old medium.
- Keep the old medium temporarily, if practical, until the new copies have passed a scheduled check. Mark its status and retirement date in the inventory.
Do not refresh all copies simultaneously without a verified intermediate copy. Staggering the work reduces the chance that one copying error or bad batch affects the entire archive.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Choosing complementary storage approaches
No single medium provides every protection. The following comparison focuses on preservation properties rather than a particular product or provider.
| Approach | Copy independence | Location separation | Fixity checking | Recovery and refresh | Cost pattern |
|---|---|---|---|---|---|
| External hard drive kept locally | Independent from the working disk if operated separately; vulnerable to the same local incident when stored beside it | None unless moved off-site | straightforward with a local manifest and scheduled full reads | Fast restoration; requires planned replacement and careful handling | Up-front device purchase, then replacement and storage costs |
| Second external drive stored elsewhere | Separate device and operator path; reduce common-cause failures by using a different manufacturer where practical | Strong physical separation when the location is genuinely independent | Possible whenever the drive is connected; logs must travel or be duplicated | Restoration may take longer because the drive must be retrieved; refresh it on the same schedule as other media | Additional hardware plus transport or custodial arrangements |
| Cloud or remote storage | Can be independent of household equipment, but the service account, credentials and provider remain dependencies | Usually provides geographic separation; confirm the service’s actual storage and recovery behavior | Use local manifests and the service’s download or verification facilities; do not assume availability of provider-side checks | Convenient remote access; migration requires downloading, verifying and possibly changing services | Recurring subscription or usage charges |
| Mirrored or redundant local array | Protects against some component failures but shares enclosure, location and administration | Usually none | Requires filesystem or application-level checks in addition to any array monitoring | Fast local failover; still needs an independent, off-site copy and a media-refresh plan | Hardware, replacement components and administration |
External hard drives and cloud storage are complementary choices: one can provide fast local recovery while the other supplies geographic separation. Whichever combination you use, retain the manifests and verify that you can actually retrieve and read a sample—or the complete set when scheduled—from each destination.
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Record format and dependency information
For each significant collection, document the file formats, versions, codecs, fonts, character encodings, database schemas, software dependencies, hardware interfaces and any passwords or keys held under an appropriate access policy. Include a short description of what a successful rendering or playback should look like. This gives a future operator a testable target rather than a folder of unexplained bytes.
Plan migration for obsolete formats
When a format, application or device is becoming difficult to obtain, identify a supported target format and preserve the original where possible. Keep the migration date, tool and settings, and calculate new checksums for both the original and the derivative. A migrated copy may be easier to open, but it is not byte-identical to the source and should never silently replace the source of record.
A routine you can operate
- At ingest: inventory files, calculate file and aggregate fixity, make three copies on two media types, verify every destination and record access dependencies.
- At each scheduled check: compare current hashes with the baseline, review unreadable or missing paths, write a dated log and investigate every mismatch.
- After a detected fault: quarantine the suspect file or device, identify a clean independent copy, restore and verify, then document the repair.
- During media refresh: check the source first, copy to a current medium, verify against the manifest, update the off-site copy and record retirement.
- During format review: test whether representative files still render or play, update dependency notes and migrate before access becomes impossible.
This routine separates three decisions that are often confused: whether the bits changed, whether a clean copy exists, and whether people can still use the format. An archive is dependable only when all three questions have an answer.
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