16GB DMA support

Dear All, We are developing a Solid State Cache usingAMD Opteron Processor with 64 bit Linux as OS. The system has 16GB SDRAM. We are plannig to use 14GB of RAM for storage and remaining for kernel and applications. Our SCSI IO Controller (FC919x) supports 64 bit dma. How we can use 14GB for storage purpose. We used pci_alloc_consistent and failed to allocate memory more than 6MB. We are allocating 512 bytes block at a time. Is there is any other optiom to use 14GB allocation for DMA. Thanks in Advance. Anurag