From owner-freebsd-fs@FreeBSD.ORG Fri Dec 25 11:11:25 2009 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A51F5106566B for ; Fri, 25 Dec 2009 11:11:25 +0000 (UTC) (envelope-from wonslung@gmail.com) Received: from mail-ew0-f226.google.com (mail-ew0-f226.google.com [209.85.219.226]) by mx1.freebsd.org (Postfix) with ESMTP id 322A08FC0C for ; Fri, 25 Dec 2009 11:11:25 +0000 (UTC) Received: by ewy26 with SMTP id 26so5443089ewy.3 for ; Fri, 25 Dec 2009 03:11:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type; bh=lq7NWErW4atTlRXyiUBq3ZumcQaAw+G/C7ZV/LW4SAM=; b=PILHJWqtYo6JvJ0F0B8db8F4TQs13PBfWs0XZwSHOu6XgY+9IldMc7NOYaGVEBdn81 zxcBj8jn9mbeXxIV0I6Ia41ygtzkqXaF7dpJeauoOYIetcKny8J/QV8gzL3x/YtzojBe A5JVwYFD/o2Ix4C9koLnpBH/jJazfBG2Li65E= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=plU+UM6qtdlOj4vxcs63oEkvrv30T42xmwVf1Vqj/0iXAtpO8INR9O2N1+AT94cqEP kqtLcDPY3H0+mgtyPD4FSrl0iaYIdd/lRnspjBjECpJNnE//LseG9KiIgbGonfhpBJiW JwCjfh60aH8eJWAKVz/e3IQTvSzHV9i/PyltE= MIME-Version: 1.0 Received: by 10.216.86.203 with SMTP id w53mr557285wee.58.1261739484092; Fri, 25 Dec 2009 03:11:24 -0800 (PST) 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> <1266543768.20091225120330@pyro.de> Date: Fri, 25 Dec 2009 06:11:24 -0500 Message-ID: From: Thomas Burgess To: Solon Lutz Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-fs@freebsd.org Subject: Re: ZFS RaidZ2 with 24 drives? X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 25 Dec 2009 11:11:25 -0000 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 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 > > > >