This paper presents the design and performance of remote disk drivers for clusters of Commodity-Off-The-Shelf PCs that fetch disk blocks over System Area Networks. The driver offers a flexible interface, being capable to logically act either as computer- or network-attached storage. It allows for fine-grain remote cache control through exclusive caching. An event-driven asynchronous block delivery mode of operation helps making the most out of the available parallelism by overlapping request processing with block delivery at both involved nodes and thus yielding better performance than local disks. The driver has been implemented as a Linux kernel module.