¿Has probado a poner un height:100% a ambos div?
<html>
<head>
<style>
#global {width:200px; height:100px; }
#left {float:left; background:#0a0; }
#right {float:right; background:#a00; }
#left, #right {height:100%; color:#fff; }
</style>
</head>
<body>
<div id="global">
<div id="left">info left</div>
<div id="right">info right</div>
</div>
</body>
</html>