zfs discuss - Mar 2009 - warm spares on a 4540

Hi,
In the doc: 
http://docs.sun.com/source/819-4359-15/CH3-maint.html#50495545_22785
of the 4540 it mentions you can have warm spares. Is there any zfs 
setting that labels a drive as a warm spare?
Or does this not matter if you use the zpool autoreplace property?

Thanks in advance,
~~sa

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Shannon A. Fiume
System Administrator
shannon dot fiume at sun dot com