Solid Archives

Solid archives compress multiple files together, achieving better compression ratios by exploiting similarities between files.

What is Solid Compression?

In a non-solid archive, each file is compressed independently:

file1.txt → [compressed data 1]
file2.txt → [compressed data 2]
file3.txt → [compressed data 3]

In a solid archive, files are concatenated and compressed together:

file1.txt + file2.txt + file3.txt → [single compressed block]

This allows the compressor to find patterns across files, significantly improving compression for similar files.

Enabling Solid Mode

use zesven::{Writer, WriteOptions, ArchivePath, Result};

fn main() -> Result<()> {
    let options = WriteOptions::new()
        .solid()
        .level(7)?;

    let mut writer = Writer::create_path("solid.7z")?
        .options(options);

    // Files will be compressed together
    writer.add_bytes(ArchivePath::new("file1.txt")?, b"Hello World")?;
    writer.add_bytes(ArchivePath::new("file2.txt")?, b"Hello World")?;  // Similar content!
    writer.add_bytes(ArchivePath::new("file3.txt")?, b"Hello World")?;

    writer.finish()?;
    Ok(())
}

Solid Block Size

Control how many files are grouped together:

use zesven::WriteOptions;
use zesven::write::SolidOptions;

let options = WriteOptions::new()
    .solid_options(SolidOptions::enabled().block_size(64 * 1024 * 1024));  // 64 MB blocks

Block Size	Compression	Extraction Speed	Memory
1 MB	Good	Fast	Low
16 MB	Better	Medium	Medium
64 MB	Best	Slower	High
Unlimited	Maximum	Slowest	Highest

Trade-offs

Advantages

• Better compression: 10-50% smaller for similar files
• Ideal for source code: Many similar files benefit greatly
• Ideal for backups: Similar file versions compress well

Disadvantages

• Slower random access: Must decompress from block start
• Higher memory: Entire block loaded for extraction
• All-or-nothing: Can't extract one file without processing the block

When to Use Solid Mode

Use solid mode for:

• Source code archives
• Document collections
• Backup archives
• Distribution packages

Avoid solid mode for:

• Archives where individual files are frequently extracted
• Archives with unrelated file types
• Situations requiring low memory extraction

Grouping Strategy

For best results, group similar files together:

use zesven::{Writer, WriteOptions, ArchivePath, Result};

fn main() -> Result<()> {
    let options = WriteOptions::new().solid();
    let mut writer = Writer::create_path("project.7z")?.options(options);

    // Group by file type for better compression
    // Source files together
    writer.add_path("src/main.rs", ArchivePath::new("src/main.rs")?)?;
    writer.add_path("src/lib.rs", ArchivePath::new("src/lib.rs")?)?;
    writer.add_path("src/utils.rs", ArchivePath::new("src/utils.rs")?)?;

    // Config files together
    writer.add_path("Cargo.toml", ArchivePath::new("Cargo.toml")?)?;
    writer.add_path("config.json", ArchivePath::new("config.json")?)?;

    // Binary files separately (don't compress well together with text)
    writer.add_path("icon.png", ArchivePath::new("icon.png")?)?;

    writer.finish()?;
    Ok(())
}

Compression Comparison

Example with 100 similar source files:

Mode	Compressed Size	Ratio
Non-solid	2.5 MB	4:1
Solid	800 KB	12:1

See Also

• Creating Archives - Basic archive creation
• Compression Options - Method and level settings
• 7z Spec: Solid Archives - Format specification