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Version Control with Subversion, 2nd Edition by Brian W. Fitzpatrick, Ben Collins-Sussman, C. Michael Pilato

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Managing Disk Space

While the cost of storage has dropped incredibly in the past few years, disk usage is still a valid concern for administrators seeking to version large amounts of data. Every bit of version history information stored in the live repository needs to be backed up elsewhere, perhaps multiple times as part of rotating backup schedules. It is useful to know which pieces of Subversion’s repository data need to remain on the live site, which need to be backed up, and which can be safely removed.

How Subversion saves disk space

To keep the repository small, Subversion uses deltification (or deltified storage) within the repository itself. Deltification involves encoding the representation of a chunk of data as a collection of differences against some other chunk of data. If the two pieces of data are very similar, this deltification results in storage savings for the deltified chunk—rather than taking up space equal to the size of the original data, it takes up only enough space to say, I look just like this other piece of data over here, except for the following couple of changes. The result is that most of the repository data that tends to be bulky—namely, the contents of versioned files—is stored at a much smaller size than the original full-text representation of that data. And for repositories created with Subversion 1.4 or later, the space savings are even better—now those full-text representations of file contents are themselves compressed.

Note

Because all of the ...

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