[Pw_forum] Fwd: help

[Paolo Giannozzi]

> From: Hüseyin Murat TÜTÜNCÜ <tutuncu at sakarya.edu.tr>
>
> In our  computer system,  different nodes have  their own  local disks
> (with scratch partition), and a rather slow communication link between
> master and slave nodes.  The present version of the pwscf code assigns
> a  single scratch  file space  (presumably at  the master  node). This
> really slows my  calculations, as well as virtually  stops other users
> from using the machine.
>
> I would  be grateful  if you  could help me  (i) identify  scratch and
> re-start data files,  and (ii) advise me how  to utilize scratch disks
> on local (i.e. slave) nodes instead of using one scratch file space on
> the master node.

in parallel execution, each processor writes its own chunk of 
wavefunctions, unless variable 'wf_collect' is specified in input. 
Wavefunctions are usually by far the largest file. All the rest 
(small files, except the charge density that becomes large only
for very large systems) is collected on a single processor and 
written there. If this slows down the calculation, either you are 
writing through the network (check where the directory pointed
by variable "outdir" resides: I/O through NFS must be avoided) 
or you have really slow communications or disks or both.

The above holds for the current version of Pwscf (3.1)
-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy