From owner-freebsd-isp@FreeBSD.ORG Tue Oct 28 08:36:20 2003 Return-Path: Delivered-To: freebsd-isp@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 8AA7D16A4CE for ; Tue, 28 Oct 2003 08:36:20 -0800 (PST) Received: from smtpout.mac.com (smtpout.mac.com [17.250.248.89]) by mx1.FreeBSD.org (Postfix) with ESMTP id 879C743FDF for ; Tue, 28 Oct 2003 08:36:19 -0800 (PST) (envelope-from cswiger@mac.com) Received: from mac.com (smtpin07-en2 [10.13.10.152]) by smtpout.mac.com (Xserve/MantshX 2.0) with ESMTP id h9SGaJ9D003870 for ; Tue, 28 Oct 2003 08:36:19 -0800 (PST) Received: from mac.com (dpvc-68-161-244-25.ny325.east.verizon.net [68.161.244.25]) (authenticated bits=0) by mac.com (Xserve/smtpin07/MantshX 3.0) with ESMTP id h9SGaICQ029399 for ; Tue, 28 Oct 2003 08:36:18 -0800 (PST) Date: Tue, 28 Oct 2003 11:36:17 -0500 Content-Type: text/plain; charset=US-ASCII; format=flowed Mime-Version: 1.0 (Apple Message framework v552) From: Charles Swiger To: freebsd-isp@freebsd.org Content-Transfer-Encoding: 7bit In-Reply-To: <20031028020239.GA74323@numenor.net> Message-Id: X-Mailer: Apple Mail (2.552) Subject: Re: consequences of migrating to maildir storage system X-BeenThere: freebsd-isp@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Internet Services Providers List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Oct 2003 16:36:20 -0000 On Monday, October 27, 2003, at 09:02 PM, Nathan Kay wrote: > That is to say, if your file system block size is 16k, and most > of the email messages are 1k, that's 15k per message (on average) that > you've lost, unless the file system is doing things to avoid it. Your thoughts are good, but note that the Unix FFS can break a 16K file system block size into eight 2K 'fragments', per "man inode": Addresses stored in inodes are capable of addressing fragments of `blocks'. File system blocks of at most size MAXBSIZE can be optionally broken into 2, 4, or 8 pieces, each of which is addressable; these pieces may be DEV_BSIZE, or some multiple of a DEV_BSIZE unit. Large files consist of exclusively large data blocks. To avoid undue wasted disk space, the last data block of a small file is allocated as only as many fragments of a large block as are necessary. The file sys- tem format retains only a single pointer to such a fragment, which is a piece of a single large block that has been divided. Also, the amount of "wasted" disk space due to intrinsic fragmentation (ie, due to the fact that files are stored in blocks leaving unused bytes after EOF) can be estimated as [ 0.5 * frag_size * number_of_files ]. -- -Chuck