[Pw_forum] Ways to reduce disk i/o when doing phonon calculations with ph.x
giannozz at democritos.it
Tue Aug 2 18:03:44 CEST 2011
On Aug 2, 2011, at 12:04 , Hans Lind wrote:
> When doing large phonon calculations (dozens of atoms, distributed
> over 1000s of nodes)
> ph.x ends up doing a very large amount of disk i/o [...]. I have
> tried setting "reduce_io='low'"
it works only for pw.x
> Or do I have to resort to using distributed disk systems?
It depends. If you have calculations involving "dozens" of atoms, you
can perform a
single irrep/wave-vector calculation on each node, working on local
disks. Then, you
have just to perform a final run that "collects" all the pieces. The
latter involves only
partial dynamical matrices, i.e. a small amount of data. The
infrastructure to do this
is in place in all recent versions, since it has been use for grid
> Are the developers working on some way to reduce the disk i/o in
> future versions?
there are projects of extending linear-response routines towards
Interested in joining the effort?
Note that there are only two ways to reduce I/O:
- store things into memory
- recalculate things instead of storing them
In the first case, you need more RAM; in the second, more CPU. No way
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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