Solid archive is an archive packed with a special compression method, which treats several or all files within the archive as one continuous data stream. WinRAR supports solid mode only in RAR archiving format, ZIP archives are always non-solid. Use Create solid archive option in archiving dialog or -s command line switch to enable solid archiving.
Solid archiving significantly increases compression when adding a large number of small, similar files. But it also has a few important disadvantages:
- slower updating of existing solid archives;
- to extract a single file from a solid archive all preceding files must be analyzed. This makes extraction from the middle of a solid archive slower than extraction from a normal archive, but, if all files are to be extracted from a solid archive, the extraction speed will not be affected.
- if any file in a solid archive is damaged, it will be impossible to extract all files which follow the damaged area. Thus if a solid archive is stored to a potentially unreliable media, it is recommended to make use of the recovery record.
Solid archiving is preferable if:
- the archive is updated rarely;
- it is not necessary to frequently extract a single file or only part of the files from the archive;
- compression ratio is more important than compression speed.