CNFS block size

Alex Kiernan alexk at
Mon Sep 9 10:17:23 UTC 2002

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.
Alex Kiernan, Principal Engineer, Development, THUS plc

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