From owner-freebsd-questions Fri Jun 7 11: 4:15 2002 Delivered-To: freebsd-questions@freebsd.org Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by hub.freebsd.org (Postfix) with ESMTP id 55D3437B403 for ; Fri, 7 Jun 2002 11:04:06 -0700 (PDT) Received: (from dan@localhost) by dan.emsphone.com (8.12.3/8.12.3) id g57I42C8082005; Fri, 7 Jun 2002 13:04:02 -0500 (CDT) (envelope-from dan) Date: Fri, 7 Jun 2002 13:04:02 -0500 From: Dan Nelson To: "Jack L. Stone" Cc: JR Richards , freebsd-questions@FreeBSD.ORG Subject: Re: Ghosting-like application Message-ID: <20020607180402.GA13099@dan.emsphone.com> References: <001801c20e48$6736bd30$3002a8c0@JR> <001801c20e48$6736bd30$3002a8c0@JR> <3.0.5.32.20020607123852.00fc2288@mail.sage-one.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3.0.5.32.20020607123852.00fc2288@mail.sage-one.net> User-Agent: Mutt/1.3.99i X-OS: FreeBSD 5.0-CURRENT X-message-flag: Outlook Error Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In the last episode (Jun 07), Jack L. Stone said: > Dan: This reminds me... I've seen the "bs=1m" all over the map from other > postings on this very subject: 1024, 4096, 8192 (even 8096)...etc. This is > the first at "1m" I've seen & still wonder how this is determined or > recommended. I'm using 8192 and it works okay. After doing a dd, I even did > a boot test on the HD #2 and it worked slick.... still wonder about the > "bs" though.... 1m is probably overkill, actually. bs= sets the read and write blocksize. When you're doing sequential I/O on large devices, raising the blocksize lowers the amount of per-read overhead the OS has to do. On my system (p3 933), a dd with an 8k blocksize takes around 7% CPU; a dd with 64k (FreeBSD splits larger bs values into multiple 64k chunks) takes 1%. On an idle system it doesn't really matter. -- Dan Nelson dnelson@allantgroup.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message