[Lustre-devel] Vector I/O api

Nikita Danilov Nikita.Danilov at Sun.COM
Sat Jul 12 10:34:09 PDT 2008

Tom.Wang writes:
 > Peter Braam wrote:
 > > Tom -
 > >
 > > In a recent call with CERN the request came up to construct a call 
 > > that can in parallel transfer an array of extents in a single file to 
 > > a list of buffers and vice-versa. 
 > > This call should be executed with read-ahead disabled, it will usually 
 > > be made when the user is well informed of the I/O that is about to 
 > > take place.
 > > Is this easy to get into the Lustre client (using our I/O library)? 
 > >  Do you have this already for MPI/IO use?
 > >
 > > Thanks.
 > >
 > > Peter
 > Hello, Peter
 > If you mean provide this list buffer read/write API in MPI by our 
 > library, it is easy.
 > Because MPI already provide such API, you can define proper 
 > discontingous buf_type
 > and file_type of these extents, and use (MPI_File_Write/read_all) to 
 > read/write these
 > buffers in one call . We only need disable read-ahead here. So it should 
 > be easy to
 > get into our I/O library.
 > But if you mean provide such API in llite, I am not sure it is easy. 
 > because it seems we

I think that if we are going to support this interface in a client, it
makes sense to implement it in CLIO. CLIO design of readv and writev
support allows upper layer (llite) to submit IO for multiple disjoint
file extents within single system call.


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