From owner-freebsd-fs@FreeBSD.ORG Fri Jul 23 13:34:42 2010 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 D36A0106566C; Fri, 23 Jul 2010 13:34:42 +0000 (UTC) (envelope-from bra@fsn.hu) Received: from people.fsn.hu (people.fsn.hu [195.228.252.137]) by mx1.freebsd.org (Postfix) with ESMTP id 1D9A98FC1A; Fri, 23 Jul 2010 13:34:41 +0000 (UTC) Received: by people.fsn.hu (Postfix, from userid 1001) id 6E1F839B2DE; Fri, 23 Jul 2010 15:34:40 +0200 (CEST) X-Bogosity: Ham, tests=bogofilter, spamicity=0.001883, version=1.2.2 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MF-ACE0E1EA [pR: 13.7865] X-CRM114-CacheID: sfid-20100723_15343_31086577 X-CRM114-Status: Good ( pR: 13.7865 ) X-DSPAM-Result: Whitelisted X-DSPAM-Processed: Fri Jul 23 15:34:40 2010 X-DSPAM-Confidence: 0.9920 X-DSPAM-Probability: 0.0000 X-DSPAM-Signature: 4c499a70132352015961825 X-DSPAM-Factors: 27, From*Attila Nagy , 0.00115, >+>, 0.00271, wrote, 0.00274, wrote, 0.00274, wrote+>, 0.00304, wrote+>, 0.00304, 8+0, 0.00631, >+I, 0.00709, 0+8, 0.00871, >+On, 0.00943, encountered, 0.01000, 9+0, 0.01000, data+is, 0.01000, it+), 0.01000, a+computer, 0.01000, stuff, 0.01000, 0+4, 0.01000, reproduce, 0.01000, reproduce, 0.01000, reading, 0.01000, reading, 0.01000, >+You, 0.01000, wouldn't, 0.01000, worse, 0.01000, cache, 0.01000, cache, 0.01000, X-Spambayes-Classification: ham; 0.00 Received: from japan.t-online.private (japan.t-online.co.hu [195.228.243.99]) by people.fsn.hu (Postfix) with ESMTPSA id D407E39B2D2; Fri, 23 Jul 2010 15:34:32 +0200 (CEST) Message-ID: <4C499A67.9080707@fsn.hu> Date: Fri, 23 Jul 2010 15:34:31 +0200 From: Attila Nagy User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.1.10) Gecko/20100629 Thunderbird/3.0.5 MIME-Version: 1.0 To: Ivan Voras References: <4C496EB0.7050004@fsn.hu> <20100723125051.GM53114@cicely7.cicely.de> <4C499733.5000104@fsn.hu> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-2; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-fs@freebsd.org Subject: Re: ZFS makes SSDs faster than memory! 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, 23 Jul 2010 13:34:42 -0000 On 07/23/10 15:29, Ivan Voras wrote: > On 07/23/10 15:20, Attila Nagy wrote: > > >> Maybe I should have written this first, but I'm not the only one reading >> from the machine. >> > You probably realize this makes all your performance data of suspicious > validity :) > Yes, this is the same I would write to this e-mail, but I can reproduce it. :) Fetching the same file not in the cache three times make the first the slowest, the second (after waiting a little to fall out of RAM) the fastest and the third the second fastest. I can consistently reproduce this behaviour, but only via network (ftpd/httpd) not from localhost. >> For random reads even the cheapest MLC outperforms a 7k2 SATA disk (only >> reads), and this is an Intel stuff, which can do 3000 RIOPS easily. >> >>> Are there any facts backup your assumption that data is really >>> read from memory, SSD, disk in the named cases? >>> E.g. by ARC/L2ARC and IO statistics. >>> >>> >> Yes. When downloading from L2ARC: >> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name >> 0 174 174 21505 0.8 0 0 0.0 13.3| ad4 >> 0 169 169 21479 0.9 0 0 0.0 15.0| ad6 >> when downloading from ARC: >> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name >> 0 26 19 1129 0.6 7 78 0.4 1.3| ad4 >> 0 19 12 1436 1.1 7 78 0.3 1.4| ad6 >> > So it looks like you encountered a problem where the memory-based ARC > cache read performance is incredibly bad? > I wouldn't call it incredibly bad, but it's worse than reading from L2ARC (2xSSD), which is pretty strange and not sane, at least to what I know about how things work in a computer. :)