A Hardware Filesystem Implementation for High-Speed Secondary Storage

Platform FPGAs are capable of hosting entire Linux- based systems including standard peripherals, integrated network interface cards and even disk controllers on a single chip. Filesystems, however, are typically implemented in software as part of the operating system. This presents a challenge as some applications are very sensitive to file I/O latency and Platform FPGA processor cores are clocked at relatively slow frequencies. This paper describes a design and implementation of a filesystem in hardware. A hardware implementation offers several features that have potential of improving certain classes of applications. The filesystem implemented is a simplified version of the well-known UNIX filesystem and specifically designed to handle a relatively low number of very large files. The design synthesizes but lacks a SATA host controller needed to test it. Instead, Modelsim was used to verify the functionality of four basic operations: open, read, write and remove. Synthesis results show that the core uses a modest 3% of the slices (and 3 BRAM blocks) of a Xilinx Virtex-4 FX60 device. By using a behavioral model of a SATA disk controller, sequential read bandwidth simulations achieved over 3 Gb/s for block sizes of 512 bytes. Since physical disks are much slower, these results suggest that a hardware filesystem core offers several benefits with little cost and no loss of performance.