Recent tumult in short-term cash markets highlights what many investors say is an inescapable fact: The plumbing underpinning US financial markets needs to be modernised. But few see an easy way to do it.

Increasing bouts of volatility in the market for Treasury repurchase agreements, or repos, stem from a system analysts and traders describe as unchanged since the 1980s, ill-suited to the postfinancial-crisis architecture and relatively manual, without public information on trades, collateral or even participants for a large chunk of transactions.