Convert RZ to 7Z Online (Swapping a Long-Range Matcher for LZMA2)

Two Formats Built by Different People to Solve Different Problems

An .rz file is the output of rzip, written by Andrew Tridgell — the same programmer behind Samba and rsync — as part of his PhD research, with its last stable release, version 2.1, dating to February 2006. It compresses in two stages: a first pass that finds repeated data across a matching window up to 900 MB, followed by a second pass running that already-shrunk data through bzip2. A .7z file is Igor Pavlov's own container format, introduced with 7-Zip in 1999, built around the LZMA and LZMA2 algorithms and capable of holding multiple files with its own central directory structure, unlike rzip's single-stream design.

Converting RZ to 7Z means running rzip's decompression in reverse to recover the original data, then compressing that recovered data from scratch using LZMA2 — there's no direct format bridge between the two, since rzip's long-range-match-plus-bzip2 approach and 7-Zip's dictionary-based LZMA2 encoding share no common intermediate representation.

This conversion also tends to happen for a practical reason rather than a purely technical one: someone received or found a .rz file, likely produced on a Linux system by a person who had rzip installed, and now needs to hand that content to a colleague or store it on a system where 7-Zip is already the standard tool — 7z's much broader install base on Windows in particular makes it the more reachable target for anyone downstream of the original file.

How LZMA2's Dictionary Compares With Rzip's Matching Window

Rzip's matching window can reach 900 MB, but that number describes the range across which it looks for repeated chunks in a single pass — it isn't a tunable dictionary the way LZMA2's is. 7-Zip's LZMA2 dictionary size is configurable up to 4 GB in current builds and scales with the compression level selected in the archiver's interface, giving a 7z conversion a dictionary that can, at the highest settings, exceed rzip's own matching range, though real-world gains depend heavily on how much RAM is actually available to back that dictionary size.

The two also diverge sharply in what they do after finding repetition. Rzip hands its de-duplicated stream to bzip2, which applies the Burrows-Wheeler transform and Huffman coding in fixed blocks around 900 KB. LZMA2 instead uses range coding directly against its dictionary matches, without the block-based restructuring bzip2 performs — a genuinely different final compression stage, not just a different implementation of the same idea.

7-Zip also applies full multithreading to LZMA2 specifically, letting a modern multi-core machine compress the recovered data significantly faster than rzip's own single-threaded design allows on the same hardware, a difference that becomes more noticeable the larger the file being converted actually is.

Rzip's compression levels run 0 (fastest) through 9 (strongest) with 6 as the default, a scale that governs how thoroughly its single matching pass searches the available window. 7-Zip's LZMA2 exposes a comparable but separately tuned range of levels, 1 through 9, and because the two algorithms work in fundamentally different ways, there's no level-for-level equivalence between an rzip setting and a 7-Zip setting that would predict matching output sizes.

What Moving From RZ to 7Z Gains and What It Costs

• Gain — far wider software support: 7-Zip, PeaZip, and many file managers open .7z natively, while .rz requires rzip itself or a specific compatible tool like PeaZip.
• Gain — native multi-file archiving: 7z's own container holds several files with individual entries and a central directory; rzip compresses only a single stream on its own.
• Gain — optional AES-256 encryption: 7z supports password-protecting both file data and, optionally, filenames themselves; rzip has no encryption feature at all.
• Gain — genuine multithreaded compression: LZMA2 in 7-Zip scales across CPU cores, while rzip's original implementation runs as a single-threaded process.
• Lose — rzip's specific long-range-matching advantage: on files with far-apart repeated data spanning hundreds of megabytes, rzip's dedicated matching pass can outperform LZMA2's dictionary on that exact kind of redundancy.
• Lose — a round trip through full decompression: since there's no shared intermediate format, converting always means fully decompressing the RZ data first and re-encoding it from raw bytes.

Which Tools Actually Handle Both Ends of an RZ-to-7Z Conversion

The original rzip binary, licensed under GPL v2 or later and packaged in Debian and Ubuntu's repositories, remains the standard way to decompress a .rz file back to its raw form, typically with rzip -d filename.rz. Once decompressed, 7-Zip (Windows) or its command-line counterpart p7zip (Linux and macOS) handles the LZMA2 compression step to produce the final .7z file — there's no single tool that performs both halves of this conversion in one pass, since rzip and 7-Zip are separate, unrelated projects.

PeaZip, the free graphical archiver for Windows and Linux, is the one program that lists native support for both formats — it can open .rz files directly and also create .7z archives, making it a practical single-application route for this specific conversion on systems that have it installed, without needing to shell out to rzip and 7-Zip separately.

Mainstream tools that many people already have installed — WinRAR, and Windows' and macOS's built-in archive handling — have no documented native support for .rz at all, meaning any conversion path that doesn't go through rzip or PeaZip specifically simply cannot read the source file in the first place.

On the 7z side, once the raw data is recovered, support is essentially universal: 7-Zip itself, PeaZip, the Files app on some Linux desktops, and Windows 11's 24H2 File Explorer update (built on the open-source libarchive project) all open .7z archives without any extra installation, a stark contrast to the small handful of programs that can even read the original .rz file.

Real Problems Reported Converting Rzip Output Into 7-Zip Archives

A recurring point of confusion involves someone assuming a newer archive tool can open a .rz file the same way it opens common formats, only to find no built-in support at all — since rzip stayed a niche Linux/Unix tool after its 2006 release and never gained the broad adoption gzip or bzip2 achieved, most general-purpose archivers besides PeaZip never implemented reading support for it.

A second documented issue involves expecting the converted 7z file to compress noticeably better than the original rz, only to see similar or occasionally worse results — this happens specifically on data whose redundancy was mostly long-range (the exact case rzip's matching window was built for), since LZMA2's dictionary, however large, isn't purpose-built the same way for repetition separated by hundreds of megabytes of unrelated bytes.

A third reported problem involves the original rzip binary failing to decompress on a system where it was installed from a very old distribution snapshot, since some older builds have known issues with specific edge-case files; the documented fix is updating to a current rzip package rather than assuming the .rz file itself is damaged.

RZ and 7Z Compared on the Details That Matter

Questions About Converting RZ Archives to 7Z

Will a 7z conversion always be smaller than the original rz file?
Not necessarily. On files whose redundancy is spread across huge distances — the specific case rzip's 900 MB matching window was designed for — the original .rz can sometimes come out smaller than a general-purpose LZMA2 pass over the same recovered data.

Is there one tool that both opens RZ and creates 7Z?
PeaZip is the one mainstream program documented to handle both — reading .rz natively and writing .7z archives — without needing to combine rzip and 7-Zip separately.

Why doesn't WinRAR open my RZ file?
WinRAR has no documented native support for the .rz extension. Rzip stayed a specialist Linux/Unix tool after its last release in 2006 and was never widely adopted into mainstream archivers.

Does converting to 7z let me add a password that RZ never supported?
Yes. 7z supports optional AES-256 encryption for file contents and, if enabled, filenames too — a feature rzip has never had at any of its compression levels.

Can 7-Zip open an RZ file directly without a separate decompression step?
No. 7-Zip has no built-in rzip support, so the original .rz file needs to be decompressed with rzip itself first before 7-Zip's LZMA2 compressor can process the recovered data.

Does the original file's content type affect how well this conversion compresses?
Yes. Database dumps, disk images, and log archives with long-range repetition tend to compress well under either format; already-compressed media inside the original .rz sees little further reduction once re-encoded as .7z.