Bad write performance with DOS based IP client.

  • 10071852
  • NOVL80472
  • 12-Jun-2002
  • 07-Aug-2002

Fact

Novell NetWare 6.0

Novell NetWare 5.1 with Support Pack 2 or higher

Novell NetWare 5.0 with Support Pack 6

TCPIP.NLM 5.22y / 5.32y or higher

Symptom

Bad write performance with DOS based IP client.

Overall write performance of an DOS based IP client is bad.

Throughput between 10 and 20 mb/min with DOS based IP client while Client32 reaches 600 mb/min on the same box.

Cause

Interoperability problems between the DOS client's IP stack and the delayed acknowledgement feature on the server. Starting with NW50SP6 / NW51SP2 delayed ACK is enabled by default on the server. While this normally gets properly negotiated it fails with certain products involved, among them the DOS IP client. Looking at the wire 200 ms delays can be seen between packets.

Fix

Disable delayed acknowledgement on the server. Since TCPIP.NLM 5.22y / 5.32y there have been three different parameters for this:
SET TCP delayed ACK = OFF (up to, but NOT including NW51SP3)
SET TCP disable delayed ACK = ON
SET TCP delayed Acknowledgement = OFF (starting with NW51SP3)
This will be in effect with the next new connection. In this case performance raised to about 220 mb/min.

Note

The DOS based IP client is NOT supported by Novell.

Disabling delayed ACK may also help in other situations, e.g. with certain backup agents or older BM proxy modules.

Disabling via SET parameter works at the transport layer, effectively turning delayed ACK of for all applications.

Delayed ACK can also be disabled at the application layer for specific tasks, leaving it on for others. An example for this are current BM proxy modules.

Even with delayed ACK disabled an IPX based DOS client will generally outperform an IP based one.