Determining SharePoint's Disk Space Needs

What you really need to keep an eye on is documents. Adding a document to a library consumes much more space than what you might think. Remember that for every document, there’s also the metadata and index data that goes with it. If a document is stored in a standard folder and has about 10 metadata properties associated with it, the document will consume about 12 KB for metadata, plus about 30% of the total document size for indexing. Therefore, if a document is 100 KB in size, you can expect to consume 100 KB for the document, 12 KB for the metadata, and 33.3 KB for the index. Your 100 KB document just consumed 145 KB

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