"Deduplication of data can be done inline, that is, before storing them."
before the words "that is" and after it.
please note that deduplication is a computer term.
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Yes: A parenthetical expression is a word or words added to a sentence without changing the meaning or grammar of the original sentence. Parenthetical expressions give extra information but are not essential.
In your example you have added "that is", to add emphasis or to clarify the condition, before storing.