From owner-freebsd-current@FreeBSD.ORG Thu Jun 9 15:36:31 2005 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1A51016A41C for ; Thu, 9 Jun 2005 15:36:31 +0000 (GMT) (envelope-from paul@gromit.dlib.vt.edu) Received: from gromit.dlib.vt.edu (gromit.dlib.vt.edu [128.173.49.29]) by mx1.FreeBSD.org (Postfix) with ESMTP id AC7B043D49 for ; Thu, 9 Jun 2005 15:36:30 +0000 (GMT) (envelope-from paul@gromit.dlib.vt.edu) Received: from zappa.Chelsea-Ct.Org (pool-151-199-7-31.ROA.east.verizon.net [151.199.7.31]) by gromit.dlib.vt.edu (8.13.3/8.13.3) with ESMTP id j59FaOkK095564 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 9 Jun 2005 11:36:25 -0400 (EDT) (envelope-from paul@gromit.dlib.vt.edu) Received: from zappa.Chelsea-Ct.Org (localhost.Chelsea-Ct.Org [127.0.0.1]) by zappa.Chelsea-Ct.Org (8.13.3/8.13.3) with ESMTP id j59FaIBC015275 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 9 Jun 2005 11:36:18 -0400 (EDT) (envelope-from paul@gromit.dlib.vt.edu) Received: (from paul@localhost) by zappa.Chelsea-Ct.Org (8.13.3/8.13.3/Submit) id j59FaGcD015274; Thu, 9 Jun 2005 11:36:16 -0400 (EDT) (envelope-from paul@gromit.dlib.vt.edu) X-Authentication-Warning: zappa.Chelsea-Ct.Org: paul set sender to paul@gromit.dlib.vt.edu using -f From: Paul Mather To: "Raphael H. Becker" In-Reply-To: <20050609113616.I41471@p-i-n.com> References: <20050608152459.BF24E16A45C@hub.freebsd.org> <1118248386.7479.10.camel@zappa.Chelsea-Ct.Org> <20050608171130.GA64736@over-yonder.net> <1118252322.7479.28.camel@zappa.Chelsea-Ct.Org> <20050609113616.I41471@p-i-n.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Thu, 09 Jun 2005 11:36:15 -0400 Message-Id: <1118331375.9927.41.camel@zappa.Chelsea-Ct.Org> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 FreeBSD GNOME Team Port Cc: freebsd-current@freebsd.org, "Matthew D. Fuller" Subject: Re: Accessing SCSI-Devices >2TB X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 09 Jun 2005 15:36:31 -0000 On Thu, 2005-06-09 at 11:36 +0200, Raphael H. Becker wrote: > So, just to work around the LBA64 problem, the idea was to recombine > those two "drives" /dev/da1 and /dev/da2 into a RAID (in FreeBSD). > > Two ways to do this: > a) striping > Every access to the logical drive in FreeBSD (/dev/ccd0) will access > both partitions PRT1 and PRT2. Remember: Every single access to ONE > of those two will result in physical disc action for PD2-PD12 and every > access to /dev/ccd0 therefore will result in two accesses for each > physical disc. --> Bad Idea. Perhaps it's because I haven't had my coffee, yet, :-) but why would this be so? If you make your stripe size large enough, you can create a hybrid effect between concatenation and striping---concatenation for smaller files and striping for larger ones. (If a file is smaller than the stripe size, access will go only to the drive on which that stripe resides. However, if it is larger, then access will be spread over multiple drives, improving load.) I am using geom_stripe on two 80 GB PATA drives to create a 120 GB stripe across both. (I only use part of each drive, and use the other part for a geom_mirror.) I have my stripe size set at 1 MB. I've been very happy with the performance. I used raidtest (now in ports) with different stripe sizes beforehand to try and ascertain a good stripe size. In my case, performance rose steadily and noticeably up to a 1 MB stripe size, and then was only slightly better as I increased thereafter. (I stopped at a 16 MB stripe.) Of course, this depends upon the kind of workload your system is expected to have. Additionally, in your case, you have the interaction with the hidden RAID 5 and whatever stripe size it is using. That possible interaction alone might be enough to use only concatenation, rendering the situation the same as using a large RAID 5. Cheers, Paul. -- e-mail: paul@gromit.dlib.vt.edu "Without music to decorate it, time is just a bunch of boring production deadlines or dates by which bills must be paid." --- Frank Vincent Zappa