A cluster file system comprises a plurality of clients and a plurality of servers configured to communicate over a network. A given server of the cluster file system interfaces with an associated storage array, and comprises a block cache and a request translator. The request translator is configured to translate input-output requests in a protocol of the cluster file system to a format suitable for use with the block cache. The cluster file system may more particularly comprise a Lustre file system, and the given server may comprise a metadata server or an object storage server of the Lustre file system. In such an embodiment, the request translator is more particularly configured to translate Lustre client input-output requests directed to the storage array into block input-output requests that are processed by the block cache. The block cache is illustratively implemented using a VFCache or other type of server flash cache.