Archiving Important Data with BDXL on macOS

September 11, 2026

Many people store family photographs, scanned documents and other important files on USB thumb drives or external hard disks, and for a good reason: both are inexpensive, convenient and capacious. Their useful life depends upon regular attention, which makes them poorly suited to unattended long-term storage. A thumb drive left in a drawer may slowly lose the electrical charges which represent its data, while a hard disk left on a shelf may suffer magnetic decay, corrosion or a mechanical failure that prevents it from spinning when it is finally needed. Irreplaceable files should consequently be preserved on additional media.

Why does flash memory lose data?

USB thumb drives, SD cards and solid-state drives use NAND flash memory, in which binary values are represented by electrons trapped within structures called floating gates. Although flash is described as non-volatile because it retains information without a continuous supply of power, the electrical charge is not permanent. Electrons escape over time, and when enough charge has been lost, the controller can no longer reliably distinguish one state from another. Temperature, the quality of the memory and the number of previous program and erase cycles all influence how quickly this process occurs.

The commonly repeated estimate that a good thumb drive may retain data for ten years comes from qualification testing across a population of components; the life of a particular consumer device will vary. As Sydney Butler explains in an overview of USB data retention, the estimate is derived from accelerated JEDEC testing in which flash is exposed to elevated temperatures. Manufacturer documentation based on similar testing generally specifies approximately ten years of retention while the memory has used less than ten percent of its rated program and erase cycles, declining to approximately one year when those cycles have been exhausted. Viking Technology's Flash Data Retention and Swissbit's discussion of NAND endurance testing provide more complete explanations of the relationship between wear and retention.

The actual retention period depends on properties that are usually unknown to the owner, particularly in inexpensive consumer devices, and an unpowered drive receives no opportunity to read, correct and rewrite weakening cells. Flash drives are consequently most useful for transferring files and maintaining actively checked copies. PCWorld reaches much the same conclusion in its discussion of charge leakage and USB drive longevity, recommending tape or optical media when truly long-term storage is required.

Are hard disks better for long-term storage?

A conventional hard disk stores data magnetically and consequently has a different collection of mechanical and electronic concerns. Data recorded on a platter can decay with time, while lubricants, bearings, heads and controller electronics continue to age even when the drive is not running. An accelerated-aging study of removable hard-disk cartridges identified magnetic thermal decay, media corrosion, evaporation of media lubricant and bearing oil, and corrosion of the electronics among the factors affecting powered-down storage. Although some removable drives performed well in the study, its small sample of conventional 3.5-inch disks exhibited substantially poorer retention, illustrating the difficulty of applying a general shelf-life estimate to an ordinary external drive.

There is also a practical distinction between preserving the information on the platter and preserving a working machine capable of retrieving it. A seized motor can make intact magnetic data inaccessible. Stored disks can provide a valuable second copy when they are periodically connected, checked and replaced. This is especially important for photographs and documents, where corruption may remain undiscovered until the original subject, camera or paper record is long gone.

What does BDXL offer?

Write-once optical media addresses these problems by recording physical changes in a layer that can be read without preserving an electrical charge or operating a complex mechanical assembly. Earlier optical formats were often impractical for large modern collections because a CD stored less than one gigabyte and a DVD generally stored less than ten. BDXL, or Blu-ray Disc XL, uses additional recording layers to provide nominal capacities of 100 GB on triple-layer media and 128 GB on quad-layer media. A modest photographic archive can therefore be written to a manageable number of discs.

Capacity and durability are separate properties. The BDXL designation describes the format and number of layers, while longevity depends upon the recording material and storage conditions. The long retention claims associated with archival optical storage generally concern M-DISC and comparable media which record data in an inorganic layer. Verbatim specifies a projected lifetime of several hundred years for its 100 GB M-DISC BDXL media, based on ISO/IEC 16963 accelerated-aging tests. Earlier ISO/IEC 10995 testing of M-DISC in the DVD format reported a mean expected life of 1,332 years at 25 °C and fifty percent relative humidity.

These figures are projections derived from exposure to elevated heat and humidity, and they should be interpreted according to the limitations of accelerated testing. Archival-grade BDXL is designed around a retention period comfortably exceeding one hundred years under suitable conditions, which makes it an attractive additional medium for photographs and records that should survive several generations. Discs should be stored vertically in individual cases, away from sunlight, excessive heat and humidity; equally important, at least two copies should be kept in different locations and checked periodically. Every preservation plan for irreplaceable information should include more than one copy.

Which drive can write archival BDXL media?

Writing multi-layer BDXL and M-DISC media requires a drive which expressly supports both formats. One capable option is the Asus BW-16D1X-U, an external USB 3 writer with support for BDXL capacities up to 128 GB and for M-DISC media. Asus lists the hardware as compatible with macOS and Windows, and a Mac recognizes the drive through its standard optical-disc support.

The difficulty for Mac users concerns the accompanying software. The principal applications supplied with the Asus drive, including CyberLink Power2Go and PowerBackup, are Windows programs; meanwhile, Apple's standard interfaces provide basic disc burning without assembling the complete archival process. Commercial Mac applications are available, but we could not find a free application that would package a large directory, create recovery data and checksums, build a correctly sized UDF image, burn it, and verify the result. It was with these requirements in mind that we created BluArchive.

How does BluArchive prepare an archive?

BluArchive is a native SwiftUI application for macOS 13 and later which coordinates the established command-line tools used by its archival process. The user selects a source directory, a staging directory, a volume label and the intended media capacity. The application can then package the source as a TAR archive, generate PAR2 recovery files, create a SHA256 manifest, build a UDF/ISO image with hdiutil makehybrid, burn the image, and verify the result. Since a large optical image requires considerable temporary space, the user chooses a staging directory on a volume with sufficient capacity.

The TAR step is recommended because it preserves the directory hierarchy and file metadata in one well-understood container. PAR2 complements this by generating recovery blocks which can reconstruct portions of a damaged archive; BluArchive uses twelve percent redundancy by default, although the value can be adjusted according to the importance of the material and the space available on the disc. A SHA256 manifest supplies a separate means of confirming that files read in the future are identical to those written today. Finally, the application reserves space for filesystem and recovery overhead when calculating payload limits for 25, 50, 100 and 128 GB media.

TAR packaging preserves the directory and its metadata in a portable archive.
PAR2 recovery data permits a limited amount of damaged data to be reconstructed.
SHA256 checksums make later verification possible.
UDF/ISO creation uses the native hdiutil makehybrid command.
Optional burning and verification use the writer selected by macOS or a specified BSD device.

BluArchive provides source, staging, TAR, PAR2 and media-capacity controls in a single window.

BluArchive burn, verify, and run backup controls — Burn speed, drive selection and verification can be configured before the archive is created.

PAR2 is available separately and can be installed through Homebrew with brew install par2. When the redundancy option is selected, BluArchive confirms the command is available during its preflight check. The application can also create and verify an ISO for later burning on another Mac.

Where can I get it?

The application and screenshots are available on the BluArchive tools page, while the complete source is maintained in the BluArchive repository on GitHub. After downloading and expanding the application, it may be necessary to right-click it and select Open the first time in order to satisfy Gatekeeper. A physical burn requires a compatible writer such as the Asus model described above, and preparation requires sufficient free disk space for the TAR file, recovery data and final ISO.

BDXL adds a durable, write-once and electrically inert copy to a preservation plan which should also include ordinary backups, periodic verification and eventual migration to new formats. For important photographs and records, that additional copy is a modest investment compared with discovering several years from now that the only thumb drive containing them can no longer be read.

Glossary

NAND flash: A form of non-volatile memory used in USB thumb drives, SD cards and solid-state drives. It records information by maintaining electrical charges within memory cells.
Floating gate: The electrically isolated part of a flash-memory cell in which electrons are trapped. The amount of charge on the floating gate determines the value stored by the cell.
Data retention: The period for which a storage medium is expected to preserve readable information without being refreshed or rewritten.
Charge leakage / bit rot: Charge leakage describes the gradual escape of electrons from a flash cell. Bit rot is a more general term for the corruption of stored information over time, regardless of the particular physical cause.
TLC / QLC: Triple-level-cell and quad-level-cell NAND store three or four bits in each cell by distinguishing several charge levels. This increases capacity and reduces cost, but leaves less margin between the electrical states than single-level-cell memory.
JEDEC: An industry standards organization which publishes procedures for qualifying electronic components. JESD47 and JESD22-A117 describe, among other things, accelerated tests used to estimate flash endurance and data retention.
Stiction: Static friction which prevents a hard-disk head or bearing from beginning to move. In severe cases the stored drive remains below operating speed and its data stays inaccessible.
BDXL: Blu-ray Disc XL, an extension of the Blu-ray format which uses three or four layers to provide nominal capacities of 100 or 128 GB. BDXL media require a compatible writer.
M-DISC: A family of archival optical media which records information in an inorganic layer. M-DISC BDXL must be written with a compatible drive, although a wider range of Blu-ray drives can read the finished disc.
BD-R: A recordable Blu-ray disc which can be written once. Its expected longevity depends upon the recording layer, manufacturing quality and storage conditions.
UDF: Universal Disk Format, a filesystem commonly used for optical data discs. BluArchive creates a UDF/ISO hybrid with the macOS hdiutil command.
TAR: A longstanding archive format which combines a directory hierarchy and its metadata into one file. BluArchive can create a TAR file before generating its recovery data and disc image.
PAR2: The second version of the Parchive recovery format. PAR2 files contain redundant blocks which can be used to reconstruct a limited amount of missing or damaged data.
SHA256 manifest: A list of cryptographic checksums calculated from the archived files. Recalculating and comparing the checksums later reveals whether the files have changed.
ISO/IEC 10995 / 16963: International standards for estimating the life of recordable optical media through accelerated exposure to heat and humidity. The results provide statistical projections for specified storage conditions.