ISO 8601 File Naming and the 3-2-1 Backup Rule for Archives

Scanning a shoebox of Kodachrome slides or nineteenth-century cabinet cards is only half of a family preservation project. Without a self-describing file-naming schema, an audited backup architecture, and museum-grade physical housing for the originals, digital scans quickly splinter into thousands of anonymous IMG_0042.jpg files scattered across aging laptops and expired cloud links. By combining ISO 8601 lexicographical file naming, CISA 3-2-1 storage capacity math, SHA-256 fixity checksums, and ISO 18916 Photographic Activity Test (PAT) enclosures, you can build a family archive that survives hardware failures and remains intelligible fifty years from now.

Why IMG_0042.jpg and Folder-Only Dates Fail in Real Life

Flatbed scanners, cameras, and transfer labs assign sequential counter names such as SCAN0001.tif or IMG_0042.jpg. Many family archivists leave those default filenames intact and rely on nested folders—such as Family Photos / 1954 / Lake George—or desktop organizers to store dates, names, and locations.

That strategy breaks the moment a file leaves your computer:

1. Texting, emailing, and cloud sharing strip folder context: When you text or email IMG_0042.jpg to a relative or upload it to an online tree, the folder path disappears. The recipient receives a bare IMG_0042.jpg with no clue about who is pictured or when it was taken.
2. Filesystem timestamps reset on copy: Operating system Date Created and Date Modified attributes record when the file was written to disk (2026-10-01), not when the wedding occurred (1948-06-12). Copying files onto an exFAT drive or uploading through a browser resets those timestamps.
3. Counter collisions overwrite scans: Every new batch restarts at SCAN0001.tif or IMG_0001.jpg, creating overwrite conflicts or IMG_0001 (1).jpg duplicates.
4. Proprietary catalog lock-in: Captions typed into a proprietary organizer stay inside an external database rather than the filename, vanishing when that software is retired.

ISO 8601 Lexicographical Date Sorting Explained

Writing dates in US middle-endian order (MM-DD-YYYY, such as 06-14-1952) or European little-endian order (DD-MM-YYYY) scrambles alphabetical file sorting. In an ASCII or UTF-8 directory listing, a computer compares characters from left to right:

Alphabetical sort of MM-DD-YYYY filenames (chronologically broken):
04-12-1985_easter-sunday.tif
06-14-1922_grandparents-wedding.tif
11-03-1944_army-furlough.tif

Because '0' precedes '1', April 1985 sorts ahead of June 1922 and November 1944.

The international standard ISO 8601 solves this by placing time units in big-endian (most-significant to least-significant) order with mandatory zero-padding: YYYY-MM-DD. Because the four-digit year occupies positions 1–4, the two-digit month occupies positions 6–7, and the two-digit day occupies positions 9–10, lexicographical character order is mathematically identical to chronological order:

Lexicographical sort of ISO 8601 YYYY-MM-DD filenames (exact chronological order):
1922-06-14_miller-arthur-benson-clara_chicago-il_wedding_001.tif
1944-11-03_miller-arthur_fort-benning-ga_furlough_001.tif
1985-04-12_miller-family_columbus-oh_easter-dinner_001.tif

Formally, for any two valid dates (Y1, M1, D1) and (Y2, M2, D2) formatted with zero-padded fields Y ∈ [0000, 9999], M ∈ [01, 12], and D ∈ [01, 31], string comparison matches integer comparison:

String("Y1-M1-D1") ≤ String("Y2-M2-D2")  ⟺  (Y1 × 10000 + M1 × 100 + D1) ≤ (Y2 × 10000 + M2 × 100 + D2)

When cataloging eighteenth-century family Bibles or colonial deeds recorded before September 1752, normalize Old Style Julian dates first using The 1752 Julian-to-Gregorian Calendar Shift and Colonial Double-Dating.

The 5-Part Archival Filename Template

Following NARA digital file-naming guidance and FADGI technical guidelines, a durable filename uses five underscore-delimited fields restricted to lowercase ASCII letters (a–z), digits (0–9), hyphens (-), and underscores (_):

YYYY-MM-DD_surname-given_location_event_seq.tif

• Field 1 (YYYY-MM-DD): Exact or approximate ISO 8601 capture date.
• Field 2 (surname-given): Primary subject’s birth/maiden surname first, followed by given name (miller-clara, or miller-family).
• Field 3 (location): Municipality and state or country code (chicago-il, cork-ie, or unknown-loc).
• Field 4 (event): Concise event or subject slug (graduation, homestead-porch, marriage-certificate).
• Field 5 (seq): Zero-padded three-digit sequence (001, 002) plus an optional side suffix (001a front/recto, 001b back/verso).

Restricting characters to [a-z0-9_-] avoids URL encoding (%20), illegal path characters (:, /, \), and Unicode normalization mismatches across macOS, Windows, and Linux NAS servers. You can generate compliant filenames interactively in the Photo, Slide & Home-Movie Digitization Planner.

Handling Approximate, Month-Only, and Decade-Only Dates

When the exact calendar day or month is unknown, preserve chronological sorting without inventing false precision by using zero-placeholder digits (1942-00-00) or trailing circa tokens (1942-00-00-ca rather than a leading ca1942 prefix):

Historical Date Certainty	Recommended Prefix	Sorting Behavior in Directory	Example Filename
Exact day known	YYYY-MM-DD	Sorts on exact day within month	1954-07-04_clark-robert_boston-ma_parade_001.tif
Year and month known	YYYY-MM-00	Sorts at top of month (00 precedes 01)	1954-07-00_clark-robert_cape-cod-ma_beach_001.tif
Year only known	YYYY-00-00	Sorts at the start of that year	1942-00-00_clark-family_boston-ma_portrait_001.tif
Circa year (±2–3 yr)	YYYY-00-00-ca	Sorts with year YYYY while flagging ca1942	1942-00-00-ca_clark-thomas_camp-polk-la_uniform_001.tif
Decade only known	YYY0-00-00-decade	Groups undated decade items at decade start	1920-00-00-decade_clark-homestead_ames-ia_barn_001.tif

Putting -ca after 1942-00-00 (1942-00-00-ca_...) rather than at the start (ca1942_...) prevents the computer from sorting the file alphabetically under C instead of chronologically between 1941 and 1943.

The CISA and Library of Congress 3-2-1 Backup Rule

Both the Library of Congress Personal Archiving guidance and CISA data backup guidance recommend the 3-2-1 backup rule:

• 3 total copies: Your primary working copy (Copy 1) plus two independent backups (Copy 2 and Copy 3).
• 2 storage media types: Combine distinct hardware technologies, such as an internal NVMe SSD (Copy 1) plus an external CMR hard disk drive or NAS (Copy 2).
• 1 offsite copy: Keep Copy 3 in a separate location—an encrypted cloud bucket or a drive stored at a relative’s home in another city—to survive fire, flood, or theft.

Storage Math: Why a 1 TB Hard Drive Holds Only 931.3 GiB

When sizing drives for a 3-2-1 archive, account for the 7.37% difference between decimal SI units (MB, GB, TB) and binary IEC units (MiB, GiB, TiB):

Decimal (Drive packaging):  1 GB = 10^9 B  |  1 TB = 10^12 B = 1,000,000,000,000 B ≈ 931.3 GiB
Binary (OS file manager):   1 GiB = 2^30 B |  1 TiB = 2^40 B = 1,099,511,627,776 B
Conversion Ratio:           1 TB / 1 GiB = 10^12 / 2^30 = 931.3226 GiB (0.9095 TiB)

Drive makers label capacity in powers of 10 (1 TB = 10^12 B ≈ 931.3 GiB), whereas operating systems divide bytes by powers of 2 (2^30 B). A "1 TB" drive displays 931.32 GiB, and a "4 TB" drive displays 3,725.29 GiB (3.638 TiB) before formatting overhead.

Worked 3-2-1 Capacity Example for a Family Estate Collection

Suppose you digitize a collection using the resolutions in Best PPI Resolution for Scanning Old Family Photos and Slides, the byte math in TIFF vs. PNG vs. JPEG: Archival File Formats and Bit-Depth Math, and the bitrates in Digitizing VHS, Hi8, MiniDV, and 8mm Home Movies:

1. 600 mounted 35mm slides (24 × 36 mm) at 4,000 PPI in 48-bit RGB TIFF (6 B/px): 3,780 × 5,669 = 21,428,820 px → 128.57 MB × 600 = 77.14 GB (71.85 GiB).
2. 1,200 prints (4×6 in) at 600 PPI (2,400 × 3,600 = 8,640,000 px) in 24-bit RGB TIFF (25.92 MB) plus JPEG access copies (2.58 MB): 28.50 MB × 1,200 = 34.20 GB (31.85 GiB).
3. 15 two-hour VHS/Hi8 tapes (30 hours) in FFV1 lossless MKV (51.75 GB/hr) plus H.264 MP4 (4.50 GB/hr): 30 hr × 56.25 GB/hr = 1,687.50 GB (1,571.61 GiB).

Single Copy (1×):   77.14 GB + 34.20 GB + 1,687.50 GB = 1,798.84 GB (1.799 TB = 1,675.30 GiB)
3-2-1 Total (3×):   1,798.84 GB × 3 copies            = 5,396.52 GB (5.397 TB = 5,025.91 GiB)

Because a "2 TB" drive offers 1,862.65 GiB raw, storing 1,675.30 GiB leaves under 9% headroom. Selecting two 4 TB CMR drives (3,725 GiB each) for Copy 1 and Copy 2, plus 1.8 TB of cloud storage for Copy 3, gives ample room.

SHA-256 Checksum Fixity Verification Against Bit Rot

Storage media can suffer silent data corruption (“bit rot”)—magnetic relaxation or charge leakage that flips a bit without raising a disk error. Without integrity checks, an automated backup script can overwrite a clean backup with a corrupted file.

Prevent silent corruption with SHA-256 fixity manifests. After scanning a batch of TIFFs, compute a 256-bit SHA-256 hash (a 64-character hex fingerprint) for each file and save it in manifest-sha256.txt:

shasum -a 256 *.tif | tee manifest-sha256.txt
shasum -a 256 -c manifest-sha256.txt

Flipping one bit inside a 128.57 MB TIFF alters roughly half of the 64 hex characters in its SHA-256 digest. Run shasum -a 256 -c semiannually before syncing Copy 1 to Copy 2 and Copy 3, and use conventional magnetic recording (CMR) hard drives for cold storage rather than unpowered flash drives.

Physical Housing Standards: PAT, Enclosures, and Climate

According to Library of Congress photograph preservation guidelines, three physical standards govern how long original prints and negatives survive:

1. ISO 18916 (Photographic Activity Test / PAT): Avoid 1970s “magnetic” sticky-line albums and PVC vinyl sleeves. Every paper envelope, box, and uncoated polyester (Mylar D / Melinex 516), polypropylene, or polyethylene sleeve must pass ISO 18916 (PAT).
2. Buffered (pH 8.5) vs. unbuffered (pH 7.0) enclosures: Use buffered (pH 8.5) paper for black-and-white silver-gelatin prints, newsprint, letters, and isolated acetate negatives, and unbuffered neutral (pH 7.0) enclosures for chromogenic color prints and slides, cyanotypes, albumen prints, and dye-transfer prints.
3. Cool, dry climate (≤ 70°F and 30–50% RH): Dye decay doubles with every 10°F (5.6°C) temperature rise. Keep archival boxes out of attics and damp basements, storing them in an interior closet at ≤ 70°F (21°C) and 30–50% RH.