143 lines
6.0 KiB
HTML
143 lines
6.0 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>Root RAID HOWTO cookbook: Introduction</TITLE>
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<LINK HREF="Root-RAID-HOWTO-2.html" REL=next>
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<LINK HREF="Root-RAID-HOWTO.html#toc1" REL=contents>
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</HEAD>
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<BODY>
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<A HREF="Root-RAID-HOWTO-2.html">Next</A>
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Previous
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<A HREF="Root-RAID-HOWTO.html#toc1">Contents</A>
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<HR>
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<H2><A NAME="s1">1. Introduction</A></H2>
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<P>The reader is assumed to be familiar with the various types of raid
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implementations, their advantages and drawbacks. This is not a tutorial,
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just a set of instructions on how to implement root mounted raid on a linux
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system. All
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of the information necessary to become familiar with linux raid is listed
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here directly or by reference, please read it before send e-mail questions.
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<P>
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<H2><A NAME="ss1.1">1.1 Where to get Up-to-date copies of this document.</A>
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</H2>
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<P>Click here to browse the
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<A HREF="ftp://ftp.bizsystems.com/pub/raid/Root-RAID-HOWTO.html">author's latest version</A> of
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this document. Corrections and suggestions welcome!
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<P>Root-RAID-HOWTO -- OBSOLETE
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<P>Available in LaTeX (for DVI and PostScript), plain text, and HTML.
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<BLOCKQUOTE>
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<A HREF="http://www.linuxdoc.org/HOWTO/Root-RAID-HOWTO.html">http://www.linuxdoc.org/HOWTO/Root-RAID-HOWTO.html</A></BLOCKQUOTE>
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Available in SGML and HTML.
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<BLOCKQUOTE>
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<A HREF="ftp://ftp.bizsystems.net/pub/raid/">ftp.bizsystems.net/pub/raid/</A></BLOCKQUOTE>
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<P>
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<A NAME="newhowto"></A> <H2><A NAME="ss1.2">1.2 More up-to-date Boot Root Raid with LILO howto</A>
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</H2>
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<P>Available in LaTeX (for DVI and PostScript), plain text, and HTML.
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<BLOCKQUOTE>
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<A HREF="http://www.linuxdoc.org/HOWTO/Boot+Root+Raid+LILO.html">http://www.linuxdoc.org/HOWTO/Boot+Root+Raid+LILO.html</A></BLOCKQUOTE>
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Available in SGML and HTML.
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<BLOCKQUOTE>
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<A HREF="ftp://ftp.bizsystems.net/pub/raid/">ftp.bizsystems.net/pub/raid/</A></BLOCKQUOTE>
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<P>
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<P>
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<H2><A NAME="ss1.3">1.3 Bugs</A>
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</H2>
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<P>As of this writing, the problem of stopping a root mounted RAID device has
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not yet been solved in a satisfactory way. A work-around proposed by Ed
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Welbon and implemented by Bohumil Chalupa is incorporated into this document
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which eliminates the need for a long ckraid at each boot for raid1 and raid5
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devices. Without the workaround, it is necessary to <B>ckraid</B> the <B>md</B> device
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each time the system is re-booted. On a large array this can cause a severe
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availability performance degradation. On my 6 gig RAID1 device running on a
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Pentium 166 with 128 megs of ram, it takes well over half an hour to ckraid
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:-(
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after each re-boot. It takes over an hour on my 13 gig RAID5 array with a
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20mb/sec scsi adaptor.
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<P>The workaround stores the status of the array at
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shutdown on the <B>real</B> boot device and compares it to a reference status
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placed there when the system is first built. If the status's match at
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reboot, the superblock on the array is rebuilt on the next boot, otherwise
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the operator is notified of the status error and the rescue system is left
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running with all the raid tools available.
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<P>Rebuilding the superblock causes
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the system to ignore that the array was powered down without mdstop by
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marking all the drives as <B>OK</B>, as if nothing happened. This only works if
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all the drives are OK at shutdown. If the array was operating with a bad
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drive, the operator must remove the bad drive prior to restarting the md
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device or the data can be corrupted.
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<P>None of this applies to raid0 which
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does not have to be mdstopped before shutdown.
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<P>Final proposed solutions to this problem include a <B>finalrd</B> similar to
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<B>initrd</B>, and <B>mdrootstop</B> which writes the <B>clean</B> flags to the array
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during shutdown when it is mounted read only. I am sure there are others.
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<P>In the mean time, the problem has been by-passed for now
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Please let me know when this problem is solved more cleanly!!!
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<P>
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<H2><A NAME="ss1.4">1.4 Acknowledgements</A>
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</H2>
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<P>The writings and e-mail from the following individuals helped to make this
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document possible. Many of the ideas were <I>stolen</I> from the helpful work of
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others, I have just tried to put it all in <B>COOKBOOK</B> form so that it is
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straightforward to use. My thanks to:
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<UL>
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<LI>
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<A HREF="mailto:linas@linas.org">Linas Vepstas</A>
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<I> for the RAID howto that explained most of this to me.</I></LI>
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<LI>
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<A HREF="mailto:gadio@netvision.net.il">Gadi Oxman</A>
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<I> for answering my dumb 'newbie' questions.</I></LI>
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<LI>
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<A HREF="mailto:welbon@bga.com">Ed Welbon</A>
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<I> for the execellent <B>initrd.md</B> package that inspired me to write this.</I></LI>
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<LI>
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<A HREF="mailto:bochal@apollo.karlov.mff.cuni.cz">Bohumil Chalupa</A> <I> for implementing the
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re-boot 'workaround' that allows</I> <B>root-mounted-raid</B><I> to
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work in a production environment.</I></LI>
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<LI>
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<A HREF="mailto:kwrohrer@ce.mediaone.net">Keith W.</A> <I> for
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his explaination of setting up root raid with </I><B> RedHat</B>.
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<P>
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</LI>
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<LI>and many others who contributed to this work in one way or another.</LI>
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</UL>
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<P>
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<H2><A NAME="ss1.5">1.5 Copyright Notice</A>
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</H2>
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<P>This document is GNU copyleft by Michael Robinton
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<A HREF="mailto:michael@bzs.org">michael@bzs.org</A>.
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<P>Permission to use, copy, distribute this document for any
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purpose is hereby granted, provided that the author's / editor's
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name and this notice appear in all copies and/or supporting
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documents; and that an unmodified version of this document is
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made freely available. This document is distributed in the hope
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that it will be useful, but WITHOUT ANY WARRANTY, either
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expressed or implied. While every effort has been taken to
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ensure the accuracy of the information documented herein, the
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author / editor / maintainer assumes NO RESPONSIBILITY for any
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errors, or for any damages, direct or consequential, as a result
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of the use of the information documented herein.
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<P>
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<HR>
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<A HREF="Root-RAID-HOWTO-2.html">Next</A>
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Previous
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<A HREF="Root-RAID-HOWTO.html#toc1">Contents</A>
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