Performance problem with indexing on a single node


We have faced some performance problems with just a single ES node. At
first when there is no data in the index the index speed is about 31Mb/s
after increasing the size of indexed data it goes to 15~20Mb/s.

we are using the elasticsearch-0.19.8 for storing and indexing our big
this is ES java options : -Xms16g -Xmx16g -Xss256k
bootstrap.mlockall: true
5 primary shards without any replica
32g ram, 8 core, 2.2T free disk space on local machine,
just one node on one machine, so there is no clustering and so on...
H.D.D write speed ~ 142Mb/s
we are using bulk add to add 10000 doc at once, the size ~ 625 Mb
one of the fields which contains almost hole the data for each record is
not supposed to index, so is set to not analyzed and not indexed. by this
it could be like writing data on disk not indexing

As you see there is no clustering, allocated memory is enough and there is
enough space on the disk.

Thank you very much.