Date: Fri, 25 Dec 2009 06:11:24 -0500 From: Thomas Burgess <wonslung@gmail.com> To: Solon Lutz <solon@pyro.de> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS RaidZ2 with 24 drives? Message-ID: <deb820500912250311y14cd0975i4e3a28c5fea24789@mail.gmail.com> In-Reply-To: <1266543768.20091225120330@pyro.de> References: <568624531.20091215163420@pyro.de> <42952D86-6B4D-49A3-8E4F-7A1A53A954C2@spry.com> <957649379.20091216005253@pyro.de> <26F8D203-A923-47D3-9935-BE4BC6DA09B7@corp.spry.com> <1696529130.20091223212612@pyro.de> <op.u5gbvfgz8527sy@82-170-177-25.ip.telfort.nl> <deb820500912241646p7c8fd726n5c68895105e28907@mail.gmail.com> <1266543768.20091225120330@pyro.de>
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Depending on tuning, you can make it flush to disk more often. It is also highly dependent on how much memory you have. What ZFS tries to do is this: It will collect stuff into memory then flush it to disk. What you describe is EXACTLY what ZFS does. Sometimes it may not write for up to 30 seconds. I know on my personal system, i see this happen a lot but it doesn't seem to have a hugely negative impact on performance for what i use my machine for. Depending on your setup, you may want to try various sysctl settings. I found that disabling prefetch can have a huge impact on some systems. On Fri, Dec 25, 2009 at 6:03 AM, Solon Lutz <solon@pyro.de> wrote: > Guten Tag Thomas Burgess, > Dear Thomas Burgess, > > am Freitag, 25. Dezember 2009 um 01:46 schrieben Sie: > on Freitag, 25. Dezember 2009 at 01:46 you wrote: > > > > On Thu, Dec 24, 2009 at 11:53 AM, Ronald Klop < > ronald-freebsd8@klop.yi.org> wrote: > > Isn't it write caching? > > My Solaris machine at work also flushes the data every 30 seconds. > > > Ronald. > > > > > I think you are right. ZFS does work in bursts...it's very different > than what most people expect. I know it was really weird to me when i > first saw it. > > But my case isn't anywhere near of performance... According to iostat and > gstat it reads > and writes some data for 3-4 seconds and then sits there silently for > another 10 and does > absolutely nothing. > Even when I'm doing single HD to single HD copy... > > > Best regards, > > Solon > > > >
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