From owner-svn-doc-head@FreeBSD.ORG Sat Dec 1 17:00:17 2012 Return-Path: Delivered-To: svn-doc-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id B061E741; Sat, 1 Dec 2012 17:00:17 +0000 (UTC) (envelope-from eadler@FreeBSD.org) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:1900:2254:2068::e6a:0]) by mx1.freebsd.org (Postfix) with ESMTP id 8BD9B8FC08; Sat, 1 Dec 2012 17:00:17 +0000 (UTC) Received: from svn.freebsd.org (localhost [127.0.0.1]) by svn.freebsd.org (8.14.5/8.14.5) with ESMTP id qB1H0H6W052077; Sat, 1 Dec 2012 17:00:17 GMT (envelope-from eadler@svn.freebsd.org) Received: (from eadler@localhost) by svn.freebsd.org (8.14.5/8.14.5/Submit) id qB1H0H3v052074; Sat, 1 Dec 2012 17:00:17 GMT (envelope-from eadler@svn.freebsd.org) Message-Id: <201212011700.qB1H0H3v052074@svn.freebsd.org> From: Eitan Adler Date: Sat, 1 Dec 2012 17:00:17 +0000 (UTC) To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r40228 - head/en_US.ISO8859-1/books/faq X-SVN-Group: doc-head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-doc-head@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: SVN commit messages for the doc tree for head List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 01 Dec 2012 17:00:17 -0000 Author: eadler Date: Sat Dec 1 17:00:17 2012 New Revision: 40228 URL: http://svnweb.freebsd.org/changeset/doc/40228 Log: Update and clarify the FAQ on soft-updates. Noted by: -stable mailing list Approved by: bcr (mentor) Modified: head/en_US.ISO8859-1/books/faq/book.xml Modified: head/en_US.ISO8859-1/books/faq/book.xml ============================================================================== --- head/en_US.ISO8859-1/books/faq/book.xml Sat Dec 1 15:51:31 2012 (r40227) +++ head/en_US.ISO8859-1/books/faq/book.xml Sat Dec 1 17:00:17 2012 (r40228) @@ -4489,24 +4489,25 @@ kern.sched.name: ULE Which partitions can safely use Soft Updates? I have heard that Soft Updates on / can cause - problems. + problems. What about Journaled Soft Updates? Short answer: you can usually use Soft Updates safely on all partitions. - Long answer: There used to be some concern over using - Soft Updates on the root partition. Soft Updates has two - characteristics that caused this. First, a Soft Updates + Long answer: Soft Updates has two + characteristics that may be undesirable on certain + paritions. First, a Soft Updates partition has a small chance of losing data during a system crash. (The partition will not be corrupted; the data will - simply be lost.) Also, Soft Updates can cause temporary + simply be lost.) Second, Soft Updates can cause temporary space shortages. When using Soft Updates, the kernel can take up to - thirty seconds to actually write changes to the physical - disk. If you delete a large file, the file still resides on + thirty seconds to write changes to the physical + disk. When a large file is deleted the file still + resides on disk until the kernel actually performs the deletion. This can cause a very simple race condition. Suppose you delete one large file and immediately create another large file. @@ -4522,20 +4523,14 @@ kern.sched.name: ULE If a system should crash after the kernel accepts a chunk of data for writing to disk, but before that data is - actually written out, data could be lost or corrupted. This - risk is extremely small, but generally manageable. Use of - IDE write caching greatly increases this risk; it is - strongly recommended that you disable IDE write caching when - using Soft Updates. + actually written out, data could be lost. This + risk is extremely small, but generally manageable. These issues affect all partitions using Soft Updates. So, what does this mean for the root partition? Vital information on the root partition changes very - rarely. Files such as - /boot/kernel/kernel and the contents of - /etc only change during system - maintenance, or when users change their passwords. If the + rarely. If the system crashed during the thirty-second window after such a change is made, it is possible that data could be lost. This risk is negligible for most applications, but you @@ -4551,6 +4546,10 @@ kern.sched.name: ULE problems. Symlinking /tmp to /var/tmp will solve this problem. + + Finally, &man.dump.8; does not work in live mode (-L) + on a filesystem, with Journaled Soft Updates + (SU+J).