Question about file allocation for recording sound data to disk

[Doug Karl]

I am in need of some advice on how to more efficently allocate a large
file (1 to 100 Mbytes) on Unix (BSD 4.3, NeXT, Sun/OS, Ultrix and System
V).  What I do on a MAC, MS-DOS and VMS is to:

	1) open a new file.
	2) lseek to the last block in the new file.
	3) write out one block.
	4) fsync, close, and reopen

Now a file is created on disk with inodes, direct and indirect blocks (or
the equivelent there of) updated and all the blocks allocated.  On Unix
that is NOT what happens, there are direct and indirect mapping blocks
that are full of zeros (ie. file is not fully mapped on disk).

So on Unix I have to:
	1) open a new file.
	2) write out each block of the file (to fully map it)
	3) fsync, close, and reopen

Is there any trick or patch to get around this?  I guess that the idea of
not actually mapping the blocks of a file on Unix until the block is
actually written to has some merrit, but is bad for me, I need to have the
file "fully" allocated quickly.

FYI. What I am doing is recording CD quality sound on a generic SCSI disk
attached to a BSD 4.3 system, NeXT, and SUN using a special SCSI disk
controller.  The special SCSI disk controller bolts on top of a 5 1/4 SCSI
drive but logically sits between the SCSI bus on the CPU and the disk(s).
This is so that the high speed data (sound in this case) can flow directly
to the disk and not load down the CPU. It is operating system and file
system independent and therefore works on Unix (assuming SCSI disks of
course).  BUT it expects that a file is fully preallocated by the
operating system (prior to recording) which takes less than a second on
VMS, MS-DOS, and MAC/OS but takes several seconds on Unix depending on
file size (because I have to write out each block of the file for it to be
"fully" allocated).  After the file is allocated then I mearly write to
the SCSI disk controller the files logical block mapping and it then can
record the sound.  Playing or re-recording is no problem since the file is
already allocated but recording a new file takes several seconds to
"setup" due to the "write each block allocation restriction (feature) of
Unix".

Please respond to me directly with ANY ideas:

karl-d at osu-20.ircc.ohio-state.edu

THANKS VERY MUCH,
Doug Karl, Instruction and Research Computer Center, Ohio State University.