ZFS performance help sought

[Michael B. Eichorn]

On Thu, 2016-01-21 at 19:05 -0500, Mason Loring Bliss wrote:
> On Thu, Jan 21, 2016 at 06:55:45PM -0500, Mason Loring Bliss wrote:
> 
> > Here's what I set:
> > 
> > vfs.zfs.arc_max="4096M"
> > vfs.zfs.arc_min="1024M"
> > vfs.zfs.txg.timeout="3"
> > vfs.zfs.write_limit_override="512M"
> > 
> > I'm not seeing any obvious way to verify the write_limit_override
> > setting -
> > it appears not to show up in sysctl output.
> > 
> > I'll wait for the current big transfer to finish and then I'll try
> > it with
> > prefetch disabled too.
> 
> Disabling prefetch doesn't do a thing here - the system is still
> painfully
> overloaded, doing something that was simply unproblematic under
> Linux.
> 
> I'd be grateful for further debugging or tuning tips. Is it possible
> this has
> nothing to do with ZFS and that I need to play with FreeBSD's
> scheduling
> somehow?
> 
> Again, FreeBSD 10.2, ZFS tuned at noted above, and with prefetch
> disabled.
> Eight gigs of RAM, pools less than 1TB. Doing a send/receive between
> pools on
> different disks is bringing the system to its knees, where the
> literal same
> hardware under Linux/ZoL doesn't break a sweat.
> 
> What else can I try?
> 

From:
freebsd.org/doc/en_US.ISO8859-1/books/handbook/zfs-advanced.html

I suppose vfs.zfs.top_maxinflight might worth a try?
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