From owner-freebsd-hardware@FreeBSD.ORG Fri Oct 31 11:57:19 2008 Return-Path: Delivered-To: freebsd-hardware@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 1FB341065690 for ; Fri, 31 Oct 2008 11:57:19 +0000 (UTC) (envelope-from numisemis@yahoo.com) Received: from web36607.mail.mud.yahoo.com (web36607.mail.mud.yahoo.com [209.191.85.24]) by mx1.freebsd.org (Postfix) with SMTP id C10798FC14 for ; Fri, 31 Oct 2008 11:57:18 +0000 (UTC) (envelope-from numisemis@yahoo.com) Received: (qmail 95792 invoked by uid 60001); 31 Oct 2008 11:57:18 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:Date:From:Reply-To:Subject:To:Cc:MIME-Version:Content-Type:Message-ID; b=Xx5P1H9N7KfCFmOVYMmufYtn1vsNP97B0b0jqM0p5M7X0X6JquHiFx7tLCBXubf0h6Q/We0DICYH3YuidGI49yCl7jLMEbQAzzSLBnmavqo7HHSPR+dFAiqUXmpxVkaOqMJUPFRndPlHMSryBp+dKxFhTd0DQtsSvwttHIGmwpk=; X-YMail-OSG: pGRKbMgVM1nnwL_FxOOUxkTIpyITRbpGf3fq_BkMuHx3YZbgjlGAwbXLMJZ8h_zlaw-- Received: from [213.147.110.159] by web36607.mail.mud.yahoo.com via HTTP; Fri, 31 Oct 2008 04:57:18 PDT X-Mailer: YahooMailWebService/0.7.260.1 Date: Fri, 31 Oct 2008 04:57:18 -0700 (PDT) From: Simun Mikecin To: Jeremy Chadwick MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Message-ID: <174490.95560.qm@web36607.mail.mud.yahoo.com> X-Mailman-Approved-At: Fri, 31 Oct 2008 12:04:34 +0000 Cc: freebsd-fs@freebsd.org, Danny Carroll , freebsd-hardware@freebsd.org Subject: Re: Areca vs. ZFS performance testing. X-BeenThere: freebsd-hardware@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: numisemis@yahoo.com List-Id: General discussion of FreeBSD hardware List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 31 Oct 2008 11:57:19 -0000 Jeremy Chadwick wrote: > Well, my understanding (which is probably wrong) is that the memory > used for the ARC is somehow separate from that of the kmap. I was > under the impression the kmap was used by ZFS for other things, and > did not include ARC. kmem is used by ARC. You can check your total kmem usage by ZFS using 'vmstat -m' under the line that says 'solaris'. > People have advocated increasing arc_min and arc_max in the past, citing > large performance gains as arc_max gets larger; you might see people > mentioning that they see great performance increases when increasing > arc_max from 64M to 128M. My understanding is that increasing the ARC > provides more actual cached data that ZFS can reference (vs. pulling it > off disk). Again, if I'm incorrect, please state so. You are correct about the benefits of increasing arc_max. I don't know of any benefits of tuning arc_min. Maybe someone else can answer this. By default on 7-STABLE arc_max will be 3/4 of kmem_size. So if you are using 1536M for kmem_size, arc_max will be 1152M by default. But some people will maybe need to lower it to avoid panic during heavy I/O since in those scenarios ARC cache size could for short periods of time be larger than arc_max and reach kmem limit.