The first syllable, "eis" (or ijs/ys), is derived from the old West Germanic word for iron.
The second syllable, "brand" (or brandt), means fire but was traditionally also used as kenning for sword.
The NRC birth registry thus suggests the meaning "iron sword".
After it had caught on as a common given name, IJsbrand remained popular throughout Dutch history and up to the present day.
According to the figures of the Sociale Verzekeringsbank [nl], the organization that implements national insurance schemes in the Netherlands, the year 2009 saw the name IJsbrand given to 4 newborn boys in The Netherlands; in the same year the alternative spelling Ysbrand had a count of 5.