How to speed up slow zpool scrub?

[Michael B. Eichorn]

On Tue, 2016-04-26 at 18:27 +0000, DH via freebsd-fs wrote:
> Take a long look at the FreeNAS documentation and discussion threads
> - if you're not using a sufficient quantity of ECC ram with ZFS
> you're asking for anomalous behavior.  I'm not a ZFS expert, but the
> documentation leads me to think inadequate system ram is certainly a
> consideration.  
> 
> FreeNAS requires a minimum of 8 GB of ECC ram when used with ZFS.

<begin friendly infodump>

It does not *need* to be ECC ram, ECC is just *highly recommended*. As
one of the key features of zfs is bitrot prevention, it makes sense to
protect against bitrot everywhere. Zfs (and thus freenas) is just fine
with non-ecc ram. Just, like for any filesystem if the bit is flipped
in ram it will be recorded as such on disk.

And 8 GB is probably a safe minumum without tuning, but there are
sufficent tunnables to do ~4 GB easily.

This is not saying that you are incorrect about best practice, I am
just picking nits since ECC and minium RAM are can be one of the more
sensitive topics for ZFS-enthusiasts.
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