Use DNFS_READBUFFERS to control the number of read buffers used by the Direct NFS Client. The Direct NFS Client is an API that can be implemented by file servers to allow improved performance when Oracle accesses files on those servers.
The default value for DNFS_READBUFFERS is 4.
Using larger values might compensate for inconsistent I/O from the Direct NFS Client file server, but it may result in increased memory usage.
Oracle Grid Infrastructure Installation Guide for Linux for information about enabling Direct NFS Client Oracle Disk Manager Control of NFS