Striped file systems such as the Parallel Virtual File System (PVFS) deliver high-bandwidth I/O to applications running on clusters. An open problem in the design of striped file systems is how to reduce their vulnerability to disk failures with the minimum performance penalty. In this paper we describe a novel data redundancy scheme designed specifically to address the performance issue. We demonstrate the new scheme within CSAR, a proof-of-concept implementation based on PVFS. By dynamically switching between RAID1 and RAID5 redundancy based on write size, CSAR consistently achieves the best of two worlds - RAID1 performance on small writes, and RAID5 efficiency on large writes. Using the popular parallel I/O benchmark BTIO, our scheme achieves 82% of the write bandwidth of the unmodified PVFS. We describe the issues in implementing our new scheme in a popular striped file system such as PVFS on a Linux cluster.