Hi,
DISK is much better for you because it will allocate all blocks at the same 
time. 
The only way to avoid the fragmentation with FILE is to pre-define all volumes.
Another thing I don't like with FILE is that you need to create more or same 
number of volumes as clients and then set number of drives. Another wise will 
you end up with queuing all backups.

PS: Most important when you pre-define any volumes for DISK or FILE is to 
create one (1) volume at the time and not all at the same time.
This can easy be done by using WAIT=YES when you create the volumes.

Best Regards
Christian Svensson

Cell: +46-70-325 1577
E-mail: Christian.Svensson AT cristie DOT se
Skype: cristie.christian.svensson
________________________________________
Från: ADSM: Dist Stor Manager [ADSM-L AT VM.MARIST DOT EDU] för Mehdi 
Salehi [iranian.aix.support AT GMAIL DOT COM]
Skickat: den 22 september 2009 07:05
Till: ADSM-L AT VM.MARIST DOT EDU
Ämne: Re: the purpose of "file" device class

Hi,
What is the technical limitation of DISK in which something like reclamation
is no possible? We have filesystem fragmentation (in OS), FILE reclamation
but nothing for DISK pools. Why?