12.1.0.2 RDBMS Clone too slow on OEL6 x86-64, runs for around 3+ hours

Command below is running for more than 3 hours on one of our system

runInstaller -clone -silent -ignorePreReq -waitForCompletion -invPtrLoc "${ORACLE_HOME}/local_inv/oraInst.loc" ORACLE_HOME="${ORACLE_HOME}" ORACLE_BASE="${HOME}" ORACLE_HOME_NAME="CLONE_OH_oh" CLUSTER_NODES={}

its a single node OEL6 x86-64, with 12102 OCT 2017 FA DBBP

On other similar systems with same kernel version it usually takes around 5-10 mins. Checked clone logs it seems to be moving but relink seems to be very slow.

OH is on NFS with mount options (rw,tcp,hard,nointr,nolock,noacl,rsize=32768,wsize=32768,nfsvers=3,timeo=600)

what could be the reason for this.