Investors in Brevan Howard, one of the hedge fund industry's biggest names, are asking for their money back.

Brevan Howard Asset Management has received redemption requests for an additional $2 billion from the firm's flagship fund this year, according to people familiar with the matter.

That fund managed about $13.7 billion as of mid-September, according to HSBC. The latest redemption requests would take the fund down to around $11.7 billion, almost half the size it was a year ago.

The Financial Times reported in early October that investors had requested at least $5 billion be returned to them. The $2 …