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Solid block size definition




What is solid compression, how to use, advantages


Solid compression option advantages and disadvantages
What is solid compression, how to use, advantages

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Solid archive definition


how to use solid compression

Solid compression is an option meant to improve data compression ratio providing a wider context for compression algorithm while compressing multiple files, which are treated as a single block rather than as separate entities.

how to set solid compression option

The ideas behind solid compression are simple and effective:
  • when multiple files are processed as a single solid block (especially similar files, i.e. same type / extension, or even revisions of the same file), it is easier to find redundant data between the files of the group, an advantage for the compression algorithm improving efficiency of compressed representation of the data, better than treating each file separately
    • solid compression is especially beneficial for archives containing multiple copies of same or very similar files, which can be archived with minimal overhead
  • when many small files are processed as a single solid block, overhead content (marker of file begin/end, checksum, table of content) is written only once rather than once per file, saving extra bytes of size for each input object - a double advantage when compressing a large number of small files, which would normally provide few context to optimize compression and will add multiple overhead content to output archive.
Solid mode is natively supported in some archival formats standards, like for 7Z and RAR file types, and is available as option in PeaZip file compression utility - it can be set in archiving screen (add to archive), "advanced options" tab.
A form of solid compression is used in compressed TAR files (TAR.GZ, TAR.BR, TAR.BZ2, TAR.ZST, TGZ, TXZ...): the data is initially added to a single container, the uncompressed tar archive, then the tar file is compressed as a single block i.e. with GZip, Brotli, BZip2, LMZA,m or Zstandard algorithm.

Main drawbacks of solid data compression are:

  • Speed performances penalities on some operations: the context information is needed both during compression / extraction to preserve the advantages of solid compression. So, the partial, selective extraction (a single file or group of file rather than the whole archive) from a solid archive, or adding or deleting files to existing archive, and updating existing files in archive needs more time on a solid archive because all the relevant context data (usually defined "solid block") must be parsed, making the process significantly slower than adding / extracting data from a non solid archive, making solid archives less simple / less fast to manage for common archiving operations
  • for the very same reason, a damage to data in any part of the archive may make all the content after that point non-usable for lack of context information needed for extraction operation, while data corruption in non solid archive usually harms only the data of a single file, with the disadvantage of solid archive being usually less resilient to suport / transmission failures and more easily severely damaged by even small loss / corruption of data.

Role of solid block size to improve compression ratio


To mitigate those disadvantages, 7Z format allows to set the block size to be used for solid mode operation (the "window" of data context that is parsed by the compression / extraction algorithm) minimizing drawbacks both in terms of overhead during extraction, and possible impact of data corruption.
However for the very same reason reducing solid block size reduces potential benefices and compression ratio improvements, providing a smaller context window to optimize the compressor algorithm.
So, the tradeoff in compression ratio vs resilience to data corruption damages, and update ease, should be accurately set.

set solid block size

Solid block "size" can be defined by size in bytes, or by number of files in a block. PeaZip file compression utility features this option in the archiving screen, advanced options tab.
An alternative optimization strategy are blocks separated by file extension, to provide more homogeneous data to each single block of the archive; this setting is also featured by PeaZip advanced compression options tab.

Read more: solid compressionconsolidate data definition on Wikipedia.

Learn how to create 7z archives with solid compression, and how to create compressed TAR archives using Brotli file compressor (very fast), BZ2 file compressor (average / good compression), GZ file compressor (fast), or Zstandard file compressor (very fast).

Synopsis: What is solid compression definition. What are advantages and disadvantages of solid data compression. How to use solid compression mode to improve compression ratio in archives containing similar files. How to define solid block size to improve compression performances with minimal decompression overhead and less speed drawbacks.

Topics: what is solid compression, solid block size, advantages and disadvantages of using solid compression

PeaZip > FAQ > What is solid compression, how to use, advantages

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