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[100.4.199.226]) by smtp.gmail.com with ESMTPSA id z65sm41026343qhc.27.2016.01.04.19.06.24 (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 04 Jan 2016 19:06:25 -0800 (PST) Subject: Re: NFS reads vs. writes Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=windows-1252 From: Paul Kraus In-Reply-To: Date: Mon, 4 Jan 2016 22:06:22 -0500 Cc: "Mikhail T." , Tom Curry Content-Transfer-Encoding: quoted-printable Message-Id: References: <8291bb85-bd01-4c8c-80f7-2adcf9947366@email.android.com> <5688D3C1.90301@aldan.algebra.com> <495055121.147587416.1451871433217.JavaMail.zimbra@uoguelph.ca> <568A047B.1010000@aldan.algebra.com> To: FreeBSD Filesystems X-Mailer: Apple Mail (2.1878.6) X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Jan 2016 03:06:27 -0000 On Jan 4, 2016, at 18:58, Tom Curry wrote: > SSDs are so fast for three main reasons: low latency, large dram = buffers, > and parallel workloads. Only one of these is of any benefit (latency) = as a > SLOG. Unfortunately that particular metric is not usually advertised = in > consumer SSDs where the benchmarks they use to tout 90,000 random = write > iops consist of massively concurrent, highly compressible, short lived > bursts of data. Add that drive as a SLOG and the onboard dram may as = well > not even exist, and queue depths count for nothing. It will be lucky = to > pull 2,000 IOPS. Once you start adding in ZFS features like checksums = and > compression, or network latency in the case of NFS that 2,000 number = starts > to drop even more. I have a file server that I am going through the task of optimizing for = NFS traffic (to store VM images). My first attempt, because I knew about = the need for an SSD based SLOG for the ZIL was using a pair of Intel 535 = series SSD=92s. The performance with the SLOG/ZIL on the SSD was = _worse_. Turns out that those SSD=92s have poor small block (8 KB) = random write performance (not well advertised). So I asked for advice = for choosing a _fast_ SSD on the OpenZFS list and had a number of people = recommend the Intel DC-Sxxxx series of SSDs. Based on the very thorough data sheets, I am going with a pair of = DC-S3710 200 GB SSDs. Once I get them in and configured I=92ll post = results. Note that my zpool consists of 5 top level vdevs each made up of a 3-way = mirror. So I am striping writes across 5 columns. I am using 500 GB WD = RE series drives leaving the ZIL on the primary vdevs was _faster_ than = adding the consumer SSD as SLOG for NFS writes. -- Paul Kraus paul@kraus-haus.org