Document the dedupditto pool property.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1839

man/man8/zpool.8

@@ -677,6 +677,17 @@ Multiple pools can share the same cache file. Because the kernel destroys and re
 A text string consisting of printable ASCII characters that will be stored such that it is available even if the pool becomes faulted.  An administrator can provide additional information about a pool using this property.
 .RE
 
+.sp
+.ne 2
+.mk
+.na
+\fB\fBdedupditto\fR=\fB\fInumber\fR\fR
+.ad
+.sp .6
+.RS 4n
+Threshold for the number of block ditto copies. If the reference count for a deduplicated block increases above this number, a new ditto copy of this block is automatically stored. The default setting is 0 which causes no ditto copies to be created for deduplicated blocks.  The miniumum legal nonzero setting is 100.
+.RE
+
 .sp
 .ne 2
 .mk