[PVFS-users] PVFS API Performance with Multiple Processes

[pvfstester at fastmail.com.au]

Sorry for the confusion. I meant "bit" as "a small peice", not as "1/8
of a byte." All writes and reads are done with buffers in the megabyte
range.

On Tue, 7 Dec 2004 10:12:37 -0600, "Robert Latham" <robl at mcs.anl.gov>
said:
> On Tue, Dec 07, 2004 at 06:14:25AM -0800, pvfstester at fastmail.com.au
> wrote:
> > I am testing out an existing piece of software which was written using
> > standard UNIX I/O and which does all of its reading and writing in large
> > blocks (multiple MB per read/write). The application is generally I/O
> > bound, and I am using a fairly large (60GB) data file to perform my
> > tests. During the course of execution, the application reads the entire
> > input file, performs some manipulation of the data, writes the file back
> > out to temporary several files a bit at a time, reads the temporary
>                                    ^^^^^^^^^^^^^
> > files back in, manipulates the data some more, and writes the data out
> > to the final output file.
> 
> Talk about a worst-case workload for pvfs1 --  or any other parallel or
> distributed file system. 
> 
> As you've seen when you wrote these temporary files to local disc,
> single-byte writes are particularly bad for pvfs1.   We do not have
> client side caching, so each byte requires a network round trip to an
> io server.  NFS caches these kinds of writes on the client side, but
> as a result, introduces consistency semantics that just won't work for
> many parallel applications.
> 
> But you said earlier in that paragraph that you read and write in
> multi-megabyte chunks, so perhaps i'm misunderstanding "bit at a
> time". 
> 
> Thanks
> ==rob
> 
> -- 
> Rob Latham
> Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
> Argonne National Labs, IL USA                B29D F333 664A 4280 315B
-- 
  
  pvfstester at fastmail.com.au