Handling Simulation Data

Versions 4.0 to latest version
Products All products
Released 4 November 2004


In some applications, the amount of data generated by a simulation can be so large that it fills up your hard disk. This article describes various methods of resolving this problem, by reducing the amount of data saved, by specifying alternative locations with more available space or by simply managing when the data files are deleted.

Where is the Data Stored?

The default location for simulation data is a system temporary directory which is usually C:\Users\[username]\AppData\Local\Temp\SIMetrixTempData. You can find out with the following sequence:

  1. Select menu File|Options|General...
  2. Select File Locations tab
  3. See the Temp Data item - this is the full path where the data files are stored

If you look in the specified folder you will notice files with the extension .sxdat are created when you run a simulation. These are the simulation data files. This directory will be cleared of all .sxdat files at certain times; exactly when is controlled by an option setting. See below for an explanation of this.

What Happens if I Run Out of Space?

On versions 5.6 and later you will likely see the error message "Disk space is too low to continue simulation." or possibly "Error initialising simulator output: There is insufficient disk space available to start the simulation.". With earlier versions you will likely get an error message "Write failure to data file" at some point during the simulation and the simulation will abort.

It is not usually possible to recover from an out of disk space condition.

How do I Fix this Problem?

There are three things that can be done to resolve this problem. Which and how many of these approaches you choose depends on the application and severity of the problem.

Delete Unused Data Files

You don't need to do this manually, you simply need to tell SIMetrix when to do it. By default, unused data files are not deleted until SIMetrix next starts. So if you keep a session of SIMetrix running for a long time (some users don't shut down for days on end) you could collect a large number of data files and eventually fill up the disk.

If this is the case, you can tell SIMetrix to delete the files when they are no longer needed. To do this, proceed as follows:

  1. Select menu File|Options|General...
  2. Select Graph/Probe/Data Analysis tab
  3. In the box titled Temporary data file delete options select When data is no longer needed

SIMetrix keeps the data for the three most recent runs always available. This allows you to retrieve the data from a recent run (using menu Simulator | Manage Data Groups...) perhaps to compare with the latest run. So with the above option set, the data files needed for the three most recent runs will always be present. If all your runs produce large amounts of data and you have no need to recover earlier data, you might like to change this behaviour so that only current data is kept. To do this, type at the command line (the edit box below the menu bar in the command shell - not available in free versions):

Set GroupPersistence=1

Make sure you spell this correctly - there will be no error message if you get it wrong.

Choose Location with More Available Space

If you have another disk/partition on your computer which has more space available, then you can tell SIMetrix to put its data there. Important: you must always use a local disk/partition; Never specify a remote network share.

To do this, proceed as follows:

  1. Select menu File|Options|General...
  2. Select File Locations tab
  3. Double click the Temp Data entry
  4. Locate a suitable path then OK

Save Less Data (SIMetrix Simulations)

The following applies to SIMetrix simulations. For SIMPLIS simulations, see next section

In some applications the only solution is to save less data in the first place. SIMetrix has comprehensive features for selecting data saved; many features are available through the GUI but some can only be selected through netlist/F11 window statements.

In the GUI select menu Simulator | Choose Analysis then click on the Data Tab. The features presented in this page allow you to reduce the amount of data which is saved automatically. You can then add keep symbols to your schematic to save specific voltages or currents that are now not automatically saved. You can also add probes to your schematic which will automatically save and plot specific voltages and currents. For keep symbols, see menus Place | Probe | Keep Voltage, Place | Probe | Keep Current and Place | Probe | Keep Inline Current.

For more sophisticated data selection features, refer to the .KEEP command in the simulator reference manual.

Save Less Data (SIMPLIS Simulations)

With SIMPLIS you can choose one of three options from the GUI. These are 'Probes Only', 'Voltages Only' and 'All'. To choose proceed as follows:

  1. Select menu Simulator|Choose Analysis...
  2. In the Save options box select All, Voltages Only or Probes Only as required. Probes Only will tell SIMetrix/SIMPLIS to save only the minimum data needed to plot any fixed probes positioned on the schematic.

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