Does FreeBSD's ZFS reserve 1/64 of the capacity for COW?

[Trond Endrestøl]

Hi,

Today I came across "Becoming a ZFS Ninja Part 1" 
http://www.youtube.com/watch?v=tPsV_8k-aVU featuring Ben Rockwood who 
stated that ZFS reserves 1/64 of the capacity for COW safe-guarding. 
Fast forward to 00:49:44. Thus, one should take this fact into account 
when planning the storage capacity of your (larger) zpools.

Does FreeBSD's ZFS also reserve 1/64 of the capacity for COW?

If it's true, then I guess this should be noted in zpool(8) and in the 
Handbook.

Any comments or insights?
Do you think I should file a PR?

Have a nice weekend! ;-)

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