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README.md: information on metadata size
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@ -113,6 +113,56 @@ ca9e19966b892d9ad5960414abac01ef585a1e22 tar-split.tar
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ca9e19966b892d9ad5960414abac01ef585a1e22 tar-split.tar.out
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ca9e19966b892d9ad5960414abac01ef585a1e22 tar-split.tar.out
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```
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```
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Stored Metadata
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---------------
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Since the raw bytes of the headers and padding are stored, you may be wondering
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what the size implications are. The headers are at least 512 bytes per
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file (sometimes more), at least 1024 null bytes on the end, and then various
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padding. This makes for a constant linear growth in the stored metadata, with a
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naive storage implementation.
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Reusing our prior example's `tar-split.tar`, let's build the checksize.go example:
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```
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go build ./checksize.go
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```
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```
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$ ./checksize ./tar-split.tar
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inspecting "tar-split.tar" (size 210k)
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-- number of files: 50
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-- size of metadata uncompressed: 53k
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-- size of gzip compressed metadata: 3k
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```
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So assuming you've managed the extraction of the archive yourself, for reuse of
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the file payloads from a relative path, then the only additional storage
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implications are as little as 3kb.
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But let's look at a larger archive, with many files.
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```
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$ ls -sh ./d.tar
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1.4G ./d.tar
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$ ./checksize ~/d.tar
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inspecting "/home/vbatts/d.tar" (size 1420749k)
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-- number of files: 38718
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-- size of metadata uncompressed: 43261k
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-- size of gzip compressed metadata: 2251k
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```
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Here, an archive with 38,718 files has a compressed footprint of about 2mb.
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Rolling the null bytes on the end of the archive, we will assume a
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bytes-per-file rate for the storage implications.
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| uncompressed | compressed |
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| :----------: | :--------: |
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| ~ 1kb per/file | 0.06kb per/file |
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What's Next?
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What's Next?
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------------
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------------
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