ZFS performance help sought

William A. Mahaffey III wam at hiwaay.net
Fri Jan 22 03:37:25 UTC 2016

On 01/21/16 14:57, Mason Loring Bliss wrote:
> Hi all.
> I've bounced back and forth between FreeBSD and Linux, and one of the reasons
> why I tend to part with FreeBSD is frustration with ZFS performance. I'm
> using my desktop for a couple roles at home. One of the roles is that it
> aggregates back-ups from across my machines and gathers them onto a back-up
> pool.
> Running FreeBSD, a zfs send/receive from one pool to another makes my system
> almost unusably slow and even begins to dig me into swap a little. As a test
> a little while back, I capped the ARC at half RAM, but that didn't matter a
> bit. I started looking into scheduler tweaking when I decided to take the
> path of least resistance and just install Linux instead. ZFS on Linux on
> literally the same hardware, dealing with the same pools, handles this same
> disk I/O without a hiccough.
> I've moved back to FreeBSD on this box now, and I'd like to resolve this
> issue. I don't know if it's a matter of fixing something broken in FreeBSD's
> scheduling or tuning ZFS somehow such that it's friendlier. (For what it's
> worth, renice'd zfs processes don't make a bit of difference, just as capping
> ARC didn't.)
> The box has FreeBSD 10.2, eight gigs of RAM, and I'm dealing with pools 1TB
> or smaller. No deduplication. I'm not enough of a ZFS guru to have a strong
> notion of what needs to change. I've not seen anything that seems
> particularly relevant in tuning guides. I have precious little diagnostic
> data to share. That said, here's a quick idea of what FreeBSD is doing,
> captured last night, with my box doing precious little else beyond the
> transfer:
> last pid:  2631;  load averages:  9.44,  8.94,  7.28    up 0+00:29:03  22:04:12
> 58 processes:  2 running, 56 sleeping
> CPU:  0.8% user,  0.0% nice, 95.8% system,  0.1% interrupt,  3.3% idle
> Mem: 136M Active, 14M Inact, 6915M Wired, 8784K Cache, 855M Free
> ARC: 6234M Total, 248M MFU, 5233M MRU, 626M Anon, 45M Header, 82M Other
> Swap: 8192M Total, 884K Used, 8191M Free
>   1334 root          1  52   15 42248K  3164K RUN     0   1:27   7.57% zfs
>   1333 root          1  38   15 42248K  3232K pipewr  1   1:04   4.98% zfs
> Not that this matters in grand scheme of things, but I'm hoping to get a
> handle on what's happening here before frustration drives me back to Linux.
> I'd be happy to gather diagnostics given some pointers on what would be
> useful. It seems unlikely that FreeBSD is this desperately inferior to Linux
> in terms of the competency of its scheduler, but I'm not sure what to tune to
> bring it up to the generally usable state I see on the same hardware under
> Linux.
> Thanks in advance!

What version of Linux, if you don't mind ? TIA & have a good one.


	William A. Mahaffey III


	"The M1 Garand is without doubt the finest implement of war
	 ever devised by man."
                            -- Gen. George S. Patton Jr.

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