rman hot backup to usb drive fails

[Knarayan]

I have mounted a usb with vfat filesystem on Red hat linux and have set the backup exports and hot_backup to the usb drive. the usb filesystem has rwx permissions for all. the exports work fine but I have having trouble with the hot backup script run as root or oracle fails with ora 27044/linux error 1perations not permitted) even though the usb filesystem is set to rwx for all.
Here is an excerpt from the hot backup log file(the same script works fine on another filesystems):RMAN-03022: compiling command: set

RMAN-03022: compiling command: backup
RMAN-03023: executing command: backup
RMAN-08008: channel d1: starting full datafile backupset
RMAN-08502: set_count=438 set_stamp=468242383 creation_time=26-JUL-02
RMAN-08010: channel d1: specifying datafile(s) in backupset
RMAN-08522: input datafile fno=00007 name=/mnt/ora_data/data01.dbf
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03007: retryable error occurred during execution of command: backup
RMAN-07004: unhandled exception during command execution on channel d1
RMAN-10035: exception raised in RPC: ORA-19504: failed to create file "/mnt/usb/
tcms_df_t468242383_s438_p1"
ORA-27044: unable to write the header block of file
Linux Error: 1: Operation not permitted
Additional information: 2
RMAN-10031: ORA-19624 occurred during call to DBMS_BACKUP_RESTORE.BACKUPPIECECRE
ATE

Recovery Manager complete.

[Knarayan]

Any suggestions please help

[marist89]

RMAN can't write to the device.