1. A method comprising: receiving at a storage server, from a requester, a request for an object stored at the server; in response to the request, determining at the storage server whether to cause a processing device in a cluster of processing devices to access the object stored at the storage server and perform an operation on the object, wherein the operation is from the set of operations consisting of virus scanning, data decompression, data encryption, and data compaction, wherein the cluster is separate from the storage server and is not in a path from the requester to the object and wherein said determining includes determining whether to cause the processing device to perform the operation based at least partially on a file space containing the object; selecting, at the storage server, the processing device from among a plurality of processing devices that form the cluster, based on a classification of the processing device relative to other processing devices in the cluster, wherein the classification is based on a performance criterion; assigning a specific access type to the processing device by the storage server when the storage server verifies the processing device satisfies restriction criteria; causing the processing device to perform the operation in response to a specified outcome of said determining; receiving at the storage server a result of the operation from the processing device; and conditionally allowing access to the object in response to the request according to the result of the operation.