CNFS block size

[Alex Kiernan]

Alex Kiernan <alexk at demon.net> writes:

> On Mon, 2002-09-09 at 01:55, Jeffrey M. Vinocur wrote:
> > 
> > So I tried CNFS with raw devices on a redhat 2.4.18-3 system.  It works.  
> > But the RAID system would like all partitions to use the same block size.  
> > (Every time a different block size is requested, it flushes the cache and 
> > spams the logfile.)  I see:
> > 
> > #define CNFS_BLOCKSIZE  512             /* Unit block size we'll work with */
> > 
> > What happens if I bump this up to 4k?
> > 
> > (And should we make this a configure option?)
> > 
> 
> Its the allocation unit within the bitmap - the bigger you make it, then
> smaller your bitmap will be (for the same size of CNFS buffer) and the
> more space you will waste after every article.
> 
> What it won't change (and I suspect this is what you think it might) is
> the size of the IO request issued - that will always be the size of an
> article, just aligned to a CNFS_BLOCKSIZE boundary.
>  

Sorry missed a bit - the IO request is the article size for writes,
for reads you get an up front small read to determine the article
size, then a full blown read/mmap.

One useful thing to look into might be to encode the article size in
the token (assuming there's enough bits left).

-- 
Alex Kiernan, Principal Engineer, Development, THUS plc