If you read there help info in the volume manager it clearly states "The Maximal NAS (NAS), iSCSI (I) and Fibre Channel (FC) volume size (with replication) is limited to 4193120MB (megabytes).

If your volume (including volume replication) fails to be created, increase the Vmalloc size. This can be done via the Hardware Console Tools (ALT+CTRL+W) -> Tuning options -> Vmalloc size."

Just RTFM.....

Sorry but dont know why people do not read it.... it was created for a reason....