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

[Trond Endrestøl]

On Fri, 6 Dec 2013 11:23-0600, Mark Felder wrote:

> 
> 
> On Fri, Dec 6, 2013, at 6:46, Trond Endrestøl wrote:
> > 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.
> > 
> 
> Well, the rule-of-thumb / urban legend tends to be "don't let your zpool
> go over ~80% or you'll have severe performance issues" so I'm not sure
> that statement is accurate or COW wouldn't be so painful when your pool
> is over ~80%. I could be wrong though; I often am :-)

As it turns out, you're in good company, I'm also wrong far too often.

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