Managing Memory and Disk Resources

There are effectively two types of data generated by an Abaqus analysis. The first is “output” data that must persist after an analysis is complete. Output data are typically either results that you require for postprocessing or data that are necessary to restart an analysis. As mentioned above, these data must be stored on disk before an analysis completes.

In addition, an analysis generates a considerable amount of “scratch” or temporary data. These are data that are needed only while an analysis is running. The scratch data can be subdivided into two groups: performance-critical data and generic data. The performance-critical data are always stored in memory, while the generic data can be stored either in memory or on disk.

To run an analysis, the following requirements must be satisfied:

• There must be sufficient disk space available to hold the requested output data.

• There must be sufficient memory available to hold all performance-critical data.

• There must be sufficient disk space or memory resource available to hold all generic scratch data.

If the above requirements are satisfied, an analysis can be completed; however, for Abaqus/Standard you may find that allowing Abaqus to use additional memory will often improve performance. With the increased availability of computer clusters, dedicated shared memory computers, and most importantly job queuing systems that allocate processors and memory for analyses, it makes most sense to be able to use all the memory resources to improve performance.

Typically Abaqus/Standard allocates a large portion of the available system memory on a machine during the analysis phase, but you can manually specify a limit for memory usage with the memory parameter (see Resource Management Parameters below). No scratch data are written to disk during the Abaqus/Explicit analysis phase, since the majority of scratch data are performance critical.

The memory parameter is used to limit the amount of memory that can be used during the analysis phase of Abaqus/Standard and during the input file processing phase, which is executed before both Abaqus/Standard and Abaqus/Explicit analyses.

If you do not define the memory parameter, Abaqus automatically detects the physical memory on the machine and allocates a percentage of this available memory. The default percentage is 80%.

You can override the default memory allocation by specifying the percent of physical memory or by specifying an absolute limit in units of megabytes or gigabytes. Percentages are indicated by a “%” sign following the specified limit. Units of megabytes and gigabytes are indicated by “mb” or “gb” following the specified limit. If no units are specified, megabytes are assumed. For example, with any of the following settings:

memory="2048 mb"
memory="2 gb"
memory="25 %"

Abaqus uses up to 2 gigabytes of memory on a machine with 8 gigabytes physical memory. The memory setting value must be surrounded by quotes. The values specified for memory must be reasonable for the machine being used. Abaqus/Standard does not check the validity of the numerical values. To be consistent with operating system memory measurement tools, a megabyte is defined by Abaqus to be 1,048,576 bytes, not 1,000,000 bytes. A similar rule applies to the unit of gigabyte.

There are no memory management parameters for the Abaqus/Explicit analysis phase, since no scratch data are written to disk during this phase.

Environment file parameters can be set for a host, for a user, or for a particular job (see Environment File Settings for further discussion). Because a default memory setting that works well for one machine with a large amount of memory may not be ideal for another machine that has less memory, it may be useful to vary the default memory settings by machine.

Management of output data is discussed in detail in About Output. Output data are written to files in the directory from which you launched the job.

Abaqus/Standard scratch files are written to a separate scratch directory. You can control the directory used to hold the scratch files with the scratch environment file parameter. Due to the frequent access of the scratch data throughout the analysis phase, ensuring high I/O speed of the scratch disks is essential to the analysis performance.

As explained above, no scratch data are written to disk for Abaqus/Explicit, so you have to be concerned only with proper management of output data.

You will usually not have to change the default memory setting. If a job fails as a result of insufficient memory with the default setting, you will need to find a machine with more memory to run the job. If you need to override the default behavior by specifying a value for the memory environment file parameter, Table 1 lists some typical data check memory settings for problems of various sizes. The actual values required for memory may vary considerably from problem to problem depending on the features used in a model.

The memory parameter allows you to specify the memory limit that can be used by Abaqus during the input file processing and analysis phases. You can specify the setting that should generally be available to Abaqus on a particular machine in the host environment file. Settings can be modified as necessary for individual jobs in job-specific environment files. Reasonable settings for a particular machine depend on the size of the problems being run and how the machine is being used in addition to the physical memory available on the machine. You should be aware of the difference between physical and virtual memory. When virtual memory is used, a machine's operating system simply uses disk for additional memory. While this can be useful, memory access may require I/O operations that add a considerable performance penalty. Therefore, the guidelines below for managing memory in Abaqus/Standard are always given relative to the physical memory on a machine. Virtual memory should be used only when necessary and with awareness of the associated performance penalty.