From owner-freebsd-fs@FreeBSD.ORG Wed May 11 13:16:27 2011 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 498841065670 for ; Wed, 11 May 2011 13:16:27 +0000 (UTC) (envelope-from alexander@leidinger.net) Received: from mail.ebusiness-leidinger.de (mail.ebusiness-leidinger.de [217.11.53.44]) by mx1.freebsd.org (Postfix) with ESMTP id F01448FC08 for ; Wed, 11 May 2011 13:16:26 +0000 (UTC) Received: from outgoing.leidinger.net (p5B155D6E.dip.t-dialin.net [91.21.93.110]) by mail.ebusiness-leidinger.de (Postfix) with ESMTPSA id E1D4F844015; Wed, 11 May 2011 15:16:12 +0200 (CEST) Received: from webmail.leidinger.net (webmail.Leidinger.net [IPv6:fd73:10c7:2053:1::2:102]) by outgoing.leidinger.net (Postfix) with ESMTP id D4A1E1279; Wed, 11 May 2011 15:16:09 +0200 (CEST) Received: (from www@localhost) by webmail.leidinger.net (8.14.4/8.13.8/Submit) id p4BDG78o064021; Wed, 11 May 2011 15:16:07 +0200 (CEST) (envelope-from Alexander@Leidinger.net) Received: from pslux.ec.europa.eu (pslux.ec.europa.eu [158.169.9.14]) by webmail.leidinger.net (Horde Framework) with HTTP; Wed, 11 May 2011 15:16:07 +0200 Message-ID: <20110511151607.105949eypk3ed3c4@webmail.leidinger.net> Date: Wed, 11 May 2011 15:16:07 +0200 From: Alexander Leidinger To: Jeremy Chadwick References: <4DCA5620.1030203@dannysplace.net> <20110511100655.GA35129@icarus.home.lan> In-Reply-To: <20110511100655.GA35129@icarus.home.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; DelSp="Yes"; format="flowed" Content-Disposition: inline Content-Transfer-Encoding: 7bit User-Agent: Dynamic Internet Messaging Program (DIMP) H3 (1.1.6) X-EBL-MailScanner-Information: Please contact the ISP for more information X-EBL-MailScanner-ID: E1D4F844015.A079B X-EBL-MailScanner: Found to be clean X-EBL-MailScanner-SpamCheck: not spam, spamhaus-ZEN, SpamAssassin (not cached, score=2.3, required 6, autolearn=disabled, MANGLED_LOAN 2.30) X-EBL-MailScanner-SpamScore: ss X-EBL-MailScanner-From: alexander@leidinger.net X-EBL-MailScanner-Watermark: 1305724573.53846@wn90bcMmycaD21chBPo8UQ X-EBL-Spam-Status: No Cc: freebsd-fs@freebsd.org Subject: Re: ZFS: How to enable cache and logs. 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: Wed, 11 May 2011 13:16:27 -0000 Quoting Jeremy Chadwick (from Wed, 11 May 2011 03:06:56 -0700): > L2ARC devices should primarily be something with extremely fast read > rates (e.g. SSDs). USB1.x and 2.x memory sticks do not work well for > this purpose given protocol and bus speed limits + overhead. (I only > mention them because people often think "Oh, USB flash would work great > for this!" I disagree.) Using USB flash may work acceptable. It depends upon the rest of the system. If you have very fast harddisks (or only USB 1 hardware), USB flash will not give you a faster FS. If you have slow (and low-power) desktop disks, a fast USB flash (attention, there are also slow ones) connected via USB 2 (or 3) will give you a speed improvement you notice. As a matter of fact, I have this: - Pentium 4 - 1 GB RAM - 1 Western Digital Caviar Blue - 2 Seagate Barracuda 7200.10 - an ICH5 controller (no NCQ) - no name cheap give-away 1 GB USB flash (so not a very fast one) The disks are used in a RAIDZ, with the USB flash as a cache device. My use case was connecting to a webmail system over a slow line (ADSL 224 kilobit/s). I noticed directly when the cache was in use or not. I also have another system, ICH 10 with NCQ, 5 disks (WD RE4 RAID) in RAIDZ2, Intel Xeon 4-core, 12 GB RAM. There USB flash does not make sense at all (and the SSD makes sense if you compare the price of the entire system with the price of a small or medium SSD). For the first system, it does not make sense to spend 200 units of money for a SSD, the system itself is not worth much more now. Spending 5-10 units of money for this system is ok, and gives a speed improvement. Bye, Alexander. -- Even God cannot change the past. -- Joseph Stalin http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID = B0063FE7 http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID = 72077137