Date: Thu, 21 Jan 2016 15:51:39 -0500 From: Mason Loring Bliss <mason@blisses.org> To: freebsd-questions@freebsd.org Subject: ZFS performance help sought Message-ID: <20160121205139.GG4538@blisses.org>
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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 PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND 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! -- Mason Loring Bliss (( "In the drowsy dark cave of the mind dreams mason@blisses.org )) build their nest with fragments dropped http://blisses.org/ (( from day's caravan." - Rabindranath Tagore
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