Thanks everyone for suggestions. This is what worked for me.
/opt/couchbase/bin/cbbackupwrapper http://11.56.24.65:8091 /Data/Backup -u yyyyy -p xxxxx -b bkt --path /opt/couchbase/bin/ --sequential -n 1024 -x cbb_max_mb=50000,batch_max_bytes=16000000,batch_max_size=5000