zfs discuss - Dec 2009 - force 4k writes?

This is most likely a naive question on my part.  If recordsize is set  
to 4k (or a multiple of 4k), will ZFS ever write a record that is less  
than 4k or not a multiple of 4k?  This includes metadata.  Does  
compression have any effect on this?

thanks for the help,
bill

On Dec 15, 2009, at 5:31 PM, Bill Sprouse wrote:
> This is most likely a naive question on my part.  If recordsize is  
> set to 4k (or a multiple of 4k), will ZFS ever write a record that  
> is less than 4k or not a multiple of 4k?
Yes.  The recordsize is the upper limit for a file record.
> This includes metadata.
Yes.  Metadata is compressed and seems to usually be one block.
> Does compression have any effect on this?
Yes. 4KB is the minimum size that can be compressed for regular data.

NB. Physical writes may be larger because they are coalesced.  But
if you are worried about recordsize, then you are implicitly worried  
about
reads.
  -- richard