Mechanical APDL Basic Analysis Guide

1. Increase the initial memory allocation via -m (for example,-m 24000). This initial memory setting
   should be larger than what the sparse solver actually requires to account for memory used prior to the
   sparse solver.


2. You can further refine sparse solver memory using the BCSOPTION command.

5.3.3. Disk Space (I/O) and Postprocessing Performance for Large Memory Problems

I/O performance with large memory One of the hidden system benefits of large memory systems
is the ability to cache large I/O requests. Even for modest-sized jobs, you can considerably reduce the
cost of I/O when the system free memory is larger than the sum of file sizes active in a job. This feature,
often called buffer cache, is a system-tunable parameter and can effectively move all I/O traffic to
memory copy speeds. The system details are different for various vendors; consult your hardware
manufacturer for details on their systems. For most Linux versions and Windows X64 systems, the be-
nefit of the system buffer cache is automatic and does not require tuning. A large memory system often
performs at almost in-core memory performance with the sparse solver when the system memory size
is larger than the matrix factorization file (usually file.LN09 or file.LN07), even when the sparse
solver runs in out-of-core mode.

5.3.4. Memory Usage on Windows 32-bit Systems

If you are running on a 32-bit Windows system, you may encounter memory problems due to Windows'
handling of contiguous memory blocks. Windows 32-bit systems limit the maximum continuous block
of memory to 2 GB; setting the /3GB switch adds another gigabyte of memory,but not contiguous with
the initial 2 GB. (See the ANSYS, Inc. Windows Installation Guide for information on setting the /3GB
switch).

Running the PCG solver with the /3GB switch set is sufficient in many situations, as is running the sparse
solver with a reasonably large -db setting and a -m setting of just 50 MB more than the -db setting.
However, to maximize your system's performance for large models, you need to:

1. Learn the largest -m you can use on your machine.


2. Learn how much memory solving your job requires.


3. Optimize your job and your system to take advantage of your system's capabilities.

Learn your -m limits To find out the largest -m setting you can use on your machine, use the following
procedure. The maximum number you determine is the upper bound on the largest contiguous block
of memory you can get on your system.

1. Open a command window and type:

ansys150 -m 1200 -db 64.

2. If that command successfully launches the Mechanical APDLprogram, close the program and repeat
   the above command, increasing the -m value by 50 each time, until the program issues an error message
   that it has insufficient memory and fails to start. Be sure to specify the same -db value each time.

Ideally, you can launch the program with a -m of 1700 or more, although 1400 is more typical. A -m
of 1200 indicat es that you may have some DLLs in your user space; contact your system administrator
for suggestions on cleaning up your user space.

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Solver Memory and Performance