This paper presents Cluster-Aware Remote Disks (CARDs), a Single System I/O architecture for cluster computing. CARDs virtualize accesses to remote cluster disks over a System Area Network. Their operation is driven by cooperative caching policies that implement a joint management of the cluster caches. All the CARDs of a given disk employ a common policy, independently of other CARD sets. CARD drivers have been implemented as Linux kernel modules which can flexibly accommodate various cooperative caching algorithms. We designed and implemented a decentralized policy called Home-based Serverless Cooperative Caching (HSCC). HSCC showed cache hit ratios over 50% for workloads that go beyond the limit of the global cache. The best speedup of a CARD over a remote disk interface was 1.54.