See the xfsctl man page from xfsprogs, specifically XFS_IOC_RESVSP
creating a sparse file will not help with fragmentation, unfortunately.
Thanks for the info, here are more specifics on what we are trying to do:
we have 200GB of harddive and would like to create 90-95 of 'video'
file, each with 2GBs (data will be writting to each file continuesly,
just like a tape). and we are hoping that if can write to the same
physical place all the time, there won't be any fragmentation problem....
we are wondering if there are any xfs parameters we can do (e.g. volumes
groups?) for the above to 'gaurantee' the best layout since we are not
going to create/delete files once created all those Video files, all we
are doing are overwriting files continuesly.