From owner-freebsd-fs@FreeBSD.ORG Fri Jul 23 13:21:30 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 76A091065672 for ; Fri, 23 Jul 2010 13:21:30 +0000 (UTC) (envelope-from freebsd-fs@m.gmane.org) Received: from lo.gmane.org (lo.gmane.org [80.91.229.12]) by mx1.freebsd.org (Postfix) with ESMTP id 3140A8FC12 for ; Fri, 23 Jul 2010 13:21:29 +0000 (UTC) Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1OcIBs-00009u-AO for freebsd-fs@freebsd.org; Fri, 23 Jul 2010 15:21:28 +0200 Received: from lara.cc.fer.hr ([161.53.72.113]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 23 Jul 2010 15:21:28 +0200 Received: from ivoras by lara.cc.fer.hr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 23 Jul 2010 15:21:28 +0200 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-fs@freebsd.org From: Ivan Voras Date: Fri, 23 Jul 2010 15:21:42 +0200 Lines: 20 Message-ID: References: <4C496EB0.7050004@fsn.hu> <4C4995F7.2080107@fsn.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: lara.cc.fer.hr User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.1.9) Gecko/20100518 Thunderbird/3.0.4 In-Reply-To: <4C4995F7.2080107@fsn.hu> X-Enigmail-Version: 1.0.1 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 13:21:30 -0000 On 07/23/10 15:15, Attila Nagy wrote: > When pulling this amount of data out of the machine, the disks aren't > saturated, they are at around 10-20% of utilization according to gstat. > BTW, remember that two RAIDZ2 in stripe isn't RAID60. In RAIDZ2 every > read involves a full stripe (er, block) read for checksum validation, > which means at a 128 kiB blocksize and with 12 disks in a RAIDZ2 pool, > all disks provide their part of that 128k read. > That's why a RAIDZ2 pool's IO performance equals of one disk's. Yes, in case of random IOPS you are correct - and in your case it would mean that the files are horribly fragmented (torrent downloads? :)). For sequential IO, even RAIDZ/1/2 will give N-1/2/3 times the performance of a single drive because prefetching will kick in. > The disks in a normal 20-30 MiBps network load do about 30-40 read IOPS, > you are right that they are capable of more (around 100-120). Except for the possible fragmentation issue, I think you should get much better throughput even with 30-40 IOPS per drive.