tar error, in pg_start_backup()

Hi All,

For some setups reason, i started taking Hot backup. In this course I have
first issued pg_start_backup('backup') and went to the data directory for
backing up in OS format using the command "tar -cf backup.tar /data" . When
i issued this command , tar was generating some errors as show below.

bash-3.00# tar -cf 16aprilstandby.tar /db-data/
tar: Removing leading `/' from member names
tar: /db-data/base/24643/151667: file changed as we read it
tar: /db-data/base/24643/151764.2: file changed as we read it
tar: /db-data/base/24643/151766: file changed as we read it
tar: /db-data/base/24643/151768: file changed as we read it
tar: /db-data/base/66412/151969: file changed as we read it

After sometime tar has ended and i also issued pg_stop_backup() and i
continued the process.

My question here is, is this errors generated by tar are to worrisome or
whats happening in the backend.
Is "tar" file is safewell to use. Could you please tell me.

Regards
Raghavendra