snapshot backup with WAL files

Hello Gurus,
I would like to configure  our Pg db for OS  file system snapshot backup 
with Pg  WAL files, need to know if would be enough in pg db   to call :
|*SELECT* *pg_start_backup*('pitr_backup');
and next take the snapshot  and after
pg_stop the backup and close the WAL files . During this time  the full 
pg  db read/writes will continue.
Are any loss of data we should may be aware during this backup procedure?
env :RHES-64 bits with LVM directories, PG 9.0, the db size >150GB
Thank you
Isabella

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Isabella A. Ghiurea 

Isabella.Ghiurea@nrc-cnrc.gc.ca
Canadian Astronomy Data Centre |http://www.nrc-cnrc.gc.ca/eng/services/hia/data-centre.html 
National Research Council of Canada, Herzberg Institute of Astrophysics 
5071 West Saanich Road, Victoria BC V9E 2E7, Canada
Phone: 250 363-3446 fax: 250 363-0045