FAQ
Short answers to common questions.
Is SQZ lossless?#
Yes, always. Every file comes back byte for byte, and SQZ checks that with BLAKE3 before it writes each file under its real name. Even the transforms that open up JPEG, PNG or ZIP files are accepted only after SQZ has rebuilt the original bytes exactly.
How is it smaller than 7-Zip?#
Three things add up: repeated data is stored once across all files and snapshots; files that are already compressed (photos, Office documents, PDFs) are opened up and compressed better, then rebuilt exactly; and Max mode can use a context-mixing engine that beats LZMA2 on text and code. On a 158.4 MB Windows app build, 7z made 79 MB and SQZ Balanced 35.1 MB.
Which mode should I use?#
Balanced for everyday use, Max for archives you keep a long time and rarely open, Fast when time matters most or the data is already compressed. See Modes and tuning.
Can someone without SQZ open my archive?#
Yes, two ways: export it with sqz zip to a standard ZIP, or send sqz-extract along with it. See Sharing archives.
Are archives encrypted?#
No. .sqz archives detect corruption but anyone can read them. sqz backup encrypts everything; see the Security model.
What happens if my computer crashes while packing?#
A new archive only appears when it is complete. An interrupted append leaves the previous snapshot readable and the next append recovers. An interrupted backup never harms earlier snapshots. See Integrity and safe restores.
Why won't SQZ extract into my folder?#
SQZ never overwrites existing files, and it checks the destination before writing anything. The error names the paths involved: usually a file that already exists, two names that differ only in letter case on a drive that ignores case, a name Windows cannot create, or too little free space. Extract into a new, empty folder, or use --file to leave out the clashing paths. The drive also has to support hard links (not FAT32 or exFAT).
How much memory does it need?#
It depends on the mode and threads, not on the amount of data. Fast needs little; Balanced, Smart and Max used 1.6 to 1.9 GB on 4 threads in our tests. Run sqz estimate for your data, and use -j to use fewer threads.
Can I pack more data than I have RAM?#
Yes. Packing and extraction stream with bounded memory.
Is the format stable?#
The archive format is versioned and specified, older versions stay readable, and a reader refuses cleanly what it does not understand. Archives made now need a current build to open. The backup repository format is still a preview and may change. See Format and compatibility.
Is there an app, or only the command line?#
Both. Archives have a Windows right-click menu, and backups have the SQZ Backup desktop app for Windows and macOS, an early preview that runs backups on a schedule.
Does it work with cloud storage?#
Backup repositories and replicas can live in S3-compatible buckets (AWS, MinIO, Ceph, Backblaze B2, Cloudflare R2). This has been tested against a simulated server but not yet a real bucket. See S3-compatible storage.
Is SQZ free?#
Yes, for personal use. Using SQZ in a business, for example at work, in a product you sell, or to back up a company's computers, needs a commercial licence. Email hello@hanki.tools. SQZ is licensed under the PolyForm Noncommercial License 1.0.0; see Licence.
Does SQZ send my data anywhere?#
No. The programs make no network connections unless you back up to an S3 bucket, and then only to that storage service, with everything encrypted first. There is no telemetry. See Privacy.
How do I get in touch?#
Email hello@hanki.tools for bug reports, questions, business and licensing enquiries, or press. For a bug, include the command you ran, the full message, your system, and what sqz-extract --version prints.
Where do I get it?#
From Getting SQZ: the full Windows package, and the extractor for Windows, Linux and macOS. They are unsigned preview builds.