Re: zpool list -p 's FREE vs. zfs list -p's AVAIL ? FREE-AVAIL == 6_675_374_080 (199G zroot pool)

Mark Millard via freebsd-current wrote:
> Context:
> 
> # gpart show -pl da0
> =>       40  468862048    da0  GPT  (224G)
>          40     532480  da0p1  efiboot0  (260M)
>      532520       2008         - free -  (1.0M)
>      534528   25165824  da0p2  swp12a  (12G)
>    25700352   25165824  da0p4  swp12b  (12G)
>    50866176  417994752  da0p3  zfs0  (199G)
>   468860928       1160         - free -  (580K)
> 
> There is just one pool: zroot and it is on zfs0 above.
> 
> # zpool list -p
> NAME           SIZE        ALLOC          FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
> zroot  213674622976  71075655680  142598967296        -         -     28     33   1.00    ONLINE  -
> 
> So FREE: 142_598_967_296
> (using _ to make it more readable)
> 
> # zfs list -p zroot 
> NAME          USED         AVAIL     REFER  MOUNTPOINT
> zroot  71073697792  135923593216     98304  /zroot
> 
> So AVAIL: 135_923_593_216
> 
> FREE-AVAIL == 6_675_374_080
> 
> 
> 
> The questions:
> 
> Is this sort of unavailable pool-free-space normal?
> Is this some sort of expected overhead that just is
> not explicitly reported? Possibly a "FRAG"
> consequence?

>From zpoolprops(8):

free    The amount of free space available in the pool.  By contrast,
        the zfs(8) available property describes how much new data can be
        written to ZFS filesystems/volumes.  The zpool free property is
        not generally useful for this purpose, and can be substantially
        more than the zfs available space. This discrepancy is due to
        several factors, including raidz parity; zfs reservation, quota,
        refreservation, and refquota properties; and space set aside by
        spa_slop_shift (see zfs-module-parameters(5) for more
        information).