Can you recommend workspace settings for a user who is running in ANSYS 8.1 in batch mode on a machine with two 1.5 GHz Itanium 64 Bit processors, running Windows XP 64-bit. It has 12 GB of RAM available. He previously ran large models in 6.1 using the -m and -db options, and everything worked fine. Now in 8.1, if he uses similar settings he receives a warning message, "...autosizing cannot allocate the needed memory..." and a page file is created.
The user does not want a page file to be used. Could you please provide more details on how and when to use the -f switch? In particular, what suggestions can you make to optimize performance with his 12 GB of RAM?
Answer from development:
The problem with Windows 64 is that the dynamic memory allocation does
not work like in all the Unix and Linux versions we have. So, a user can still
use the extra memory but with some extra issues. Avoiding a page file is not necessarily the
best thing to do to optimize performance anymore. It is more important to
leave enough memory so the solver can go very fast than to use it all for
keeping the entire database in memory. Some post processing operations will
work a lotbetter with the very large db file but I would post process
separately anyway for very large models. I.e. solve first, save the db and
resume it in a separate step.
What I would do on a Win64 machine with 12 Gbytes of memory is first to see if my large
job would run well with a starting memory usage of -m 8192 -db 1024. Leave the
rest of the memory for the system and I/O cache. Most jobs will run very well
in 8 Gbytes. Even if you manage to grab all of the 12 Gbytes for ANSYS that doesn't
mean the performance will be great. If you choke the OS using up all the memory
the ansys PERFORMANCE WON'T BE REAL GOOD.
Don't just set -db in these runs. Set -m as well and ignore that message we put out about
not needing it anymore. That message is true for most systems and optimal for
the pcg solver when memory can grow dynamically on a system. But, Win64 is probably
better off if you ask for the memory up front..