Solid archives

Solid archiving is a compression method that treats all files as a single continuous data stream, achieving significantly better compression ratios.

What are Solid Archives?

In a solid archive, files are compressed together as one continuous block:

All files are treated as a single data stream
Compression dictionary is shared across files
Similar data patterns across files are efficiently compressed
Maximum compression ratio is achieved

Solid vs Non-Solid

Feature	Solid Archive	Non-Solid Archive
Compression ratio	Excellent (10-50% better)	Good
Random access	Slower	Fast
Update speed	Slower	Fast
Memory usage	Higher	Lower
Best for	Backups, distribution	Frequent updates

Creating Solid Archives

# Enable solid mode
7z a -ms=on archive.7z files/

# With maximum compression
7z a -ms=on -mx=9 archive.7z files/

Solid mode is enabled by default for 7z archives. Use -ms=off to disable it.

Solid Block Size

You can control the solid block size for better balance between compression and access speed:

# 1MB solid blocks
7z a -ms=1m archive.7z files/

# 16MB solid blocks
7z a -ms=16m archive.7z files/

# 1GB solid blocks (maximum compression)
7z a -ms=1g archive.7z files/

# Unlimited (all files in one block)
7z a -ms=on archive.7z files/

Choosing Block Size

Small blocks (1-16 MB)
Medium blocks (64-512 MB)
Large blocks (1GB+)

Best for: Archives with frequent random access

7z a -ms=16m archive.7z files/

Faster extraction of individual files
Lower memory usage
Slightly worse compression

Best for: Balanced compression and access

7z a -ms=512m archive.7z files/

Good compression ratio
Reasonable extraction speed
Moderate memory usage

Best for: Maximum compression, infrequent access

7z a -ms=on archive.7z files/

Maximum compression ratio
Slower individual file extraction
Higher memory usage

Compression Example

Non-Solid Archive

# Compress files individually
7z a -ms=off archive.7z files/

Each file is compressed independently:

file1.txt → LZMA → compressed block 1
file2.txt → LZMA → compressed block 2
file3.txt → LZMA → compressed block 3

Solid Archive

# Compress all files together
7z a -ms=on archive.7z files/

All files compressed as one stream:

file1.txt + file2.txt + file3.txt → LZMA → compressed block

Compression improvement example:

1000 text files (1 KB each) = 1 MB total
Non-solid: ~400 KB (40% compression)
Solid: ~100 KB (90% compression)

The improvement comes from sharing the compression dictionary across similar files.

Memory Requirements

Solid compression requires more memory:

Compression Memory

Memory = DictionarySize × (10 to 20)

Example with 64 MB dictionary:

Non-solid: ~100 MB
Solid: ~1.2 GB

Decompression Memory

Memory = DictionarySize + SolidBlockSize

Example:

Dictionary: 64 MB
Solid block: 512 MB
Required memory: ~576 MB

Extraction Performance

Extracting Single File

Non-solid:

# Fast - only decompress one file
7z x archive.7z specific-file.txt

Solid:

# Slower - must decompress all files before the target
7z x archive.7z specific-file.txt

Extracting All Files

Both solid and non-solid have similar performance when extracting all files:

# Extract everything
7z x archive.7z

Solid Archive Organization

By File Type

Organize files by type for better compression:

# Group similar files
7z a -ms=on archive.7z *.txt *.log *.xml *.json

By Extension

Use solid groups to compress similar files together:

# Solid blocks per extension
7z a -ms=e archive.7z files/

This creates separate solid blocks for each file extension.

Custom Sorting

# Sort by extension then name
7z a -ms=on archive.7z -stl files/

Solid Archives with Filters

Combine solid compression with BCJ filters for executables:

# Solid archive with x86 filter
7z a -ms=on -mf=BCJ archive.7z *.exe *.dll

This provides excellent compression for collections of similar executables.

Best Practices

Use solid archives for:

Backup archives
Software distribution
Large collections of similar files
Long-term storage
Maximum compression priority

Avoid solid archives for:

Frequently updated archives
Archives needing random access
Low-memory systems
Incremental backups

Advanced Examples

Maximum Compression Backup

7z a -t7z -mx=9 -md=64m -mfb=273 -ms=on -mmt=on backup.7z /data/

Partly-Solid Archive

# 512 KB solid blocks
7z a -ms=512k -mx=9 archive.7z files/

Balances compression ratio and extraction speed.

Solid Archive with Header Encryption

7z a -ms=on -mhe=on -p archive.7z files/

Maximum compression with full encryption.

Implementation Details

Solid compression in 7-Zip:

Implemented in CPP/7zip/Archive/7z/7zHandler.cpp
Solid block structure in CPP/7zip/Archive/7z/7zFolderOutStream.cpp
Memory management in CPP/7zip/Common/

From DOC/readme.txt (lines 36-42):

If you have big number of files in archive, and you need fast extracting,
you can use partly-solid archives:

  7za.exe a archive.7z *.htm -ms=512K -r -mx -m0fb=255 -m0d=512K

In that example 7-Zip will use 512KB solid blocks. So it needs to decompress
only 512KB for extracting one file from such archive.

Getting Started

Command Reference

Compression Methods

Archive Formats

Advanced Usage

Solid archives

What are Solid Archives?

Solid vs Non-Solid

Creating Solid Archives

Solid Block Size

Choosing Block Size

Compression Example

Non-Solid Archive

Solid Archive

Memory Requirements

Compression Memory

Decompression Memory

Extraction Performance

Extracting Single File

Extracting All Files

Solid Archive Organization

By File Type

By Extension

Custom Sorting

Solid Archives with Filters

Best Practices

Advanced Examples

Maximum Compression Backup

Partly-Solid Archive

Solid Archive with Header Encryption

Implementation Details

See Also

​What are Solid Archives?

​Solid vs Non-Solid

​Creating Solid Archives

​Solid Block Size

​Choosing Block Size

​Compression Example

​Non-Solid Archive

​Solid Archive

​Memory Requirements

​Compression Memory

​Decompression Memory

​Extraction Performance

​Extracting Single File

​Extracting All Files

​Solid Archive Organization

​By File Type

​By Extension

​Custom Sorting

​Solid Archives with Filters

​Best Practices

​Advanced Examples

​Maximum Compression Backup

​Partly-Solid Archive

​Solid Archive with Header Encryption

​Implementation Details

​See Also

What are Solid Archives?

Solid vs Non-Solid

Creating Solid Archives

Solid Block Size

Choosing Block Size

Compression Example

Non-Solid Archive

Solid Archive

Memory Requirements

Compression Memory

Decompression Memory

Extraction Performance

Extracting Single File

Extracting All Files

Solid Archive Organization

By File Type

By Extension

Custom Sorting

Solid Archives with Filters

Best Practices

Advanced Examples

Maximum Compression Backup

Partly-Solid Archive

Solid Archive with Header Encryption

Implementation Details

See Also