Reading and writing a large file

[Allison Holloway <ahollowa-hcNo3dDEHLuVc3sceRu5cw@public.gmane.org>]

Hi,

I want to run a program in NILFS that performs lots of random and 
sequential reads and writes on a large file.  The program uses pread64 
and pwrite64 to do the file accesses; I'm accessing the data 32KB at a 
time, and I give the location as the logical offset within the file.  It 
works fine on my department's AFS file system, but I'm having 2 issues 
with NILFS:
1) pwrite64 will sometimes fail, and I haven't figured out what it 
correlates to.  I know sometimes it's because the disk has run out of 
room, but I'm not sure that that is always the cause.
2) Garbage collection/ cleanup.  After enough blocks of the file have 
been rewritten (possibly multiple times), I'll get a disk full error.  
Then, even if I've deleted all the files in my nilfs partition, I cannot 
create a new non-empty file.  Is there a way to speed up the garbage 
collection process, or better interleave it with the program so I don't 
get these "disk full" errors?

Any help or insight you could give would be greatly appreciated!

Thank you,
Allison