S7 driver optimization tips?

I have a gateway with 7 Siemens S7-400 PLC to connect with the Siemens drivers.
I/O sqltag will be about 70.000 (7* 10.000) and I need the best reponse time possible.
All the date are in DB area.

Do I need to create 1 device for 1 PLC or multiple device for 1 PLC ?
With each device corresponding to separate DB or fraction of a DB.

If 1 device is 1 thread or 1 socket, perhaps more thread or socket will help ?

Start with creating 1 device per PLC and if you find the performance isn’t acceptable you can start splitting it into multiple devices.

Hi Kevin,

Result of my test for a Proof Of Concept to validate Ignition for a new project :
about 72.000 io tags spreed on 7-10 Redundant PLC Siemens S7-400

My POC : Ignition 7.6.6
with a PLC S7-400 conected to Ignition with Siemens S7-400 PLCs over Ethernet Device.

I try 7200 io Tag @500 ms
I adjust the PDU value to 480 ? An error log if the value is superior to 480.
What is it exactly.
Does the PDU value depends from the type of Siemens CPU ???

Result are ok with 7200 tag, so I continue…
I added 7200 io tag @500ms, for a total of 14400 io.
I don’t have tag deconnection but request duration have increased.

So I create a second device for the same PLC as follow :
=> 7200 io tag for device [S7400] (ip =
=> 7200 io tag for device [S74002] (ip =
the request duration are better.

For my POC, I have only 1 PLC, and i need to test 72.000 iotag, so i will split it in 10 devices and see the results.

My big problem is about writing resquest.
I have a script to test big writing request : 10 values, 100 values, …
We will have scenario with batch of command and large parameters table to write into the PLCs.

For my test, I use only 1 system.tag.writeAll with a table of tags and a table of values.
It’s very long, about 10 sec for 10 values ! with more values I receive timeout.
It’s seem to be a synchronous writing ??? I would like a bulk write of all the value.
How can I optimize that ???
These kind of writing are very fast for memory tag or opc tag with other driver.
The limitation is relative to the S7 driver ?

I await your lights…

Best Regards.

Have you ever complete your tests and came to conclusions?
I’m interested…
BTW, your pictures (attachments) are not shown.

We have switch to kep server siemens drivers which enable more optimization options and manage the switch btw 2 redundant plc
If ignition is selected for the project with s7 plc, we will do more test soon.
You can post me a PM