Block_Size on NTFS

Hi all !

Reading through the list of settings returned by "SHOW ALL", I noticed
the "block_size" variable, which defaults to 8192.

Running on Windows Server, my data directory is on an NTFS partition.
Running CHKDSK on this partition tells me that there are "4096 bytes in
each allocation unit."

Are these allocation units the same as the "block_size", or does this
only have to do with disk geometry ?
If they are the same, is it important that they match ?

Thanks for your help !

Regards,
--
Arnaud Lesauvage