204 lines
7.6 KiB
HTML
204 lines
7.6 KiB
HTML
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<!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>HOWTO: Multi Disk System Tuning: Bits and Pieces </TITLE>
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<LINK HREF="Multi-Disk-HOWTO-21.html" REL=next>
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<LINK HREF="Multi-Disk-HOWTO-19.html" REL=previous>
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<LINK HREF="Multi-Disk-HOWTO.html#toc20" REL=contents>
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</HEAD>
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<BODY>
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<A HREF="Multi-Disk-HOWTO-21.html">Next</A>
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<A HREF="Multi-Disk-HOWTO-19.html">Previous</A>
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<A HREF="Multi-Disk-HOWTO.html#toc20">Contents</A>
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<HR>
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<H2><A NAME="bits-n-pieces"></A> <A NAME="s20">20. Bits and Pieces </A></H2>
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<P>
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<!--
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disk!miscellaneous
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-->
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This is basically a section where I stuff all the bits I have not yet
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decided where should go, yet that I feel is worth knowing about. It is
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a kind of transient area.
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<P>
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<P>
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<P>
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<H2><A NAME="ss20.1">20.1 Swap Partition: to Use or Not to Use</A>
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</H2>
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<P>
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<!--
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disk!miscellaneous!swap or no swap
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-->
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In many cases you do not need a swap partition, for instance if you
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have plenty of RAM, say, more than 64 MB, and you are the sole user
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of the machine. In this case you can experiment running without a
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swap partition and check the system logs to see if you ran out of
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virtual memory at any point.
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<P>Removing swap partitions have two advantages:
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<UL>
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<LI>you save disk space (rather obvious really)</LI>
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<LI>you save seek time as swap partitions otherwise would
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lie in the middle of your disk space.</LI>
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</UL>
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<P>In the end, having a swap partition is like having a heated toilet:
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you do not use it very often, but you sure appreciate it when
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you require it.
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<P>
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<H2><A NAME="ss20.2">20.2 Mount Point and <CODE>/mnt</CODE></A>
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</H2>
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<P>
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<!--
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disk!miscellaneous!mount point issues
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-->
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In an earlier version of this document I proposed to put all
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permanently mounted partitions under <CODE>/mnt</CODE>. That, however, is
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not such a good idea as this itself can be used as a mount point, which
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leads to all mounted partitions becoming unavailable. Instead I will
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propose mounting straight from root using a meaningful name like
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<CODE>/mnt.descriptive-name</CODE>.
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<P>Lately I have become aware that some Linux distributions use mount points
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at subdirectories <EM>under</EM> <CODE>/mnt</CODE>, such as <CODE>/mnt/floppy</CODE>
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and <CODE>/mnt/cdrom</CODE>, which just shows how confused the whole issue is.
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Hopefully FHS should clarify this.
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<P>
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<P>
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<H2><A NAME="power-heating"></A> <A NAME="ss20.3">20.3 Power and Heating </A>
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</H2>
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<P>
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<!--
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disk!miscellaneous!power-related issues
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-->
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<!--
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disk!miscellaneous!heat-related issues
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-->
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Not many years ago a machine with the equivalent power of a modern PC
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required 3-phase power and cooling, usually by air conditioning the machine
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room, some times also by water cooling. Technology has progressed very
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quickly giving not only high speed but also low power components. Still,
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there is a definite limit to the technology, something one should keep in
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mind as the system is expanded with yet another disk drive or PCI
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card. When the power supply is running at full rated power, keep in mind
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that all this energy is going somewhere, mostly into heat. Unless this is
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dissipated using fans you will get a serious heating inside the cabinet
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followed by a reduced reliability and also life time of the electronics.
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Manufacturers state minimum cooling requirements for their drives, usually
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in terms of cubic feet per minute (CFM). You are well advised to take this
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serious.
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<P>Keep air flow passages open, clean out dust and check the temperature of your
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system running. If it is too hot to touch it is probably running too hot.
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<P>If possible use sequential spin up for the drives. It is during
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spin up, when the drive platters accelerate up to normal speed,
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that a drive consumes maximum power and if all drives start up
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simultaneously you could go beyond the rated power maximum of
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your power supply.
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<P>
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<H2><A NAME="ss20.4">20.4 Deja</A>
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</H2>
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<P>
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<!--
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disk!miscellaneous!Dejanews
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-->
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<!--
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disk!miscellaneous!Deja
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-->
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<!--
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disk!reliability
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-->
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This is an Internet system that no doubt most of you are familiar with.
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It searches and serves <EM>Usenet News</EM> articles from 1995 and to the
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latest postings and also offers a web based reading and posting interface.
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There is a lot more, check out
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<A HREF="http://www.deja.com">Deja</A>
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for more information. It changed name from Dejanews.
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<P>What perhaps is less known, is that they use about 120 Linux SMP
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computers many of which use the <CODE>md</CODE> module to manage between 4
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and 24 Gig of disk space (over 1200 Gig altogether) for this service.
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The system is continuously growing but at the time of writing they
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use mostly dual Pentium Pro 200MHz and Pentium II 300 MHz
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systems with 256 MB RAM or more.
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<P>A production database machine normally has 1 disk for the operating system and
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between 4 and 6 disks managed by the <CODE>md</CODE> module where the articles are
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archived.
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The drives are connected to BusLogic Model BT-946C and BT-958
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PCI SCSI adapters, usually one to a machine.
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<P>For the production
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systems (which are up 365 days a year) the downtime attributable to
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disk errors is less than 0.25 % (that is a quarter of 1%, not 25%).
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<P>Just in case: this is not an advertisement, it is stated as an
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example of how much is required for what is a major Internet
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service.
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<P>
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<P>
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<P>
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<H2><A NAME="ss20.5">20.5 Crash Recovery</A>
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</H2>
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<P>
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<!--
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disk!miscellaneous!recovery
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-->
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<!--
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disk!miscellaneous!crash recovery
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-->
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Occationally hard disks crash. A crash causing data scrambling can
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often be at least partially recovered from and there are already
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HOWTOs describing this.
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<P>In case of hardware failure things are far more serious, and you
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have two options: either send the drive to a professional data
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recovery company, or try recovering yourself. The latter is of
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course <EM>high risk</EM> and can cause more damage.
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<P>If a disk stops rotating or fails to spin up, the number one
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advice is first to turn off the system as fast as safely possible.
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<P>Next you could try disconnecting the drives and power up the
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machine, just to check power with a multimeter that power is
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present. Quite often connectors can get unseated and cause all
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sorts of problems.
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<P>If you decide to risk trying it yourself you could check all
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connectors and then reapply power and see if the drive spins up
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and responds. If it still is dead turn off power quickly,
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preferrably before the operating system boots. Make sure that
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delayed spinup is not deceiving you here.
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<P>If you decide to progress even further (and take higher risks)
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you could remove the drive, give it a firm tap on the side so
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that the disk moves a little with respect to the casing. This
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can help in unsticking the head from the surface, allowing the
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platter to move freely as the motor power is not sufficient to
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unstick a stuck head on its own.
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<P>Also if a drive has been turned off for a while after running
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for long periods of time, or if it has overheated, the lubricant
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can harden of drain out of the bearings. In this case warming the
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drive slowly and gently up to normal operating temperature will
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possibly recover the lubrication problems.
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<P>If after this the drive still does not respond the last possible
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and the highest risk suggestion is to replace the circuit board
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of the drive with a board from am identical model drive.
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<P>Often the contents of a drive is worth far more than the media
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itself, so do consider professional help. These companies have
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advanced equipment and know-how obtained from the manufacturers
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on how to recover a damaged drive, far beyond that of a hobbyist.
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<P>
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<P>
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<P>
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<P>
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<HR>
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<A HREF="Multi-Disk-HOWTO-21.html">Next</A>
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|
<A HREF="Multi-Disk-HOWTO-19.html">Previous</A>
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|
<A HREF="Multi-Disk-HOWTO.html#toc20">Contents</A>
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</BODY>
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</HTML>
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