Slow backups following migration from emc clarion cx4-120 to VNX 5400

We are currently using backup exec 2010 for our backups and are backing up to tape. The server we are having problems with is an oracle database server, getting backed up with the oracle agent. The backup speed has decreased from 4GB per minute to 400MB per minute after migrating it to the new storage. Other aspects have remained exactly the same. When we moved the oracle database back to the cx4 the speed increases. This would indicate a problem with the new SAN, has anyone else experienced any problems following migration to VNX 5400?