[Pw_forum] Ways to reduce disk i/o when doing phonon calculations with ph.x

[Paolo Giannozzi]

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  
computing.

> 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  
large systems.
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  
out.

P.
---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222