993 lines
20 KiB
HTML
993 lines
20 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>LVM 2 FAQ</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="LVM HOWTO"
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HREF="faq.html"><LINK
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TITLE="LVM 1 FAQ"
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HREF="lvm1faq.html"></HEAD
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BGCOLOR="#FFFFFF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>LVM HOWTO</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="faq.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 4. Frequently Asked Questions</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="lvm1faq.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="sect1"
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><H1
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CLASS="sect1"
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><A
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NAME="lvm2faq"
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></A
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>4.1. LVM 2 FAQ</H1
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><DIV
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CLASS="qandaset"
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><DL
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><DT
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>4.1.1. <A
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HREF="lvm2faq.html#AEN279"
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> I have LVM 1 installed and running on my system. How do
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I start using LVM 2?
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</A
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></DT
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><DT
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>4.1.2. <A
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HREF="lvm2faq.html#AEN298"
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> Do I need a special lvm2 kernel module?
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</A
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></DT
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><DT
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>4.1.3. <A
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HREF="lvm2faq.html#AEN303"
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> I get errors about
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<TT
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CLASS="filename"
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>/dev/mapper/control</TT
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> when I try to
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use the LVM 2 tools. What's going on?
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</A
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></DT
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><DT
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>4.1.4. <A
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HREF="lvm2faq.html#AEN326"
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> Which commands and types of logical volumes are
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currently supported in LVM 2?
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</A
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></DT
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><DT
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>4.1.5. <A
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HREF="lvm2faq.html#AEN338"
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> Does LVM 2 use a different format from LVM 1 for it's
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ondisk representation of Volume Groups and Logical
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Volumes?
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</A
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></DT
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><DT
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>4.1.6. <A
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HREF="lvm2faq.html#AEN343"
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> Does LVM 2 support VGs and LVs created with LVM 1?
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</A
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></DT
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><DT
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>4.1.7. <A
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HREF="lvm2faq.html#AEN348"
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> Can I upgrade my LVM 1 based VGs and LVs to LVM 2 native
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format?
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</A
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></DT
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><DT
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>4.1.8. <A
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HREF="lvm2faq.html#AEN353"
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> I've upgraded to LVM 2, but the tools keep failing with out
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of memory errors. What gives?
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</A
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></DT
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><DT
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>4.1.9. <A
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HREF="lvm2faq.html#AEN359"
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> I have my root partition on an LV in LVM 1. How do I
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upgrade to LVM 2? And what happened to lvmcreate_initrd?
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</A
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></DT
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><DT
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>4.1.10. <A
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HREF="lvm2faq.html#AEN383"
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> How resilient is LVM to a sudden renumbering of
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physical hard disks?
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</A
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></DT
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><DT
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>4.1.11. <A
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HREF="lvm2faq.html#AEN391"
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> I'm trying to fill my vg, and vgdisplay/vgs says that I
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have 1.87 GB free, but when I do an lvcreate vg -L1.87G
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it says "insufficient free extends". What's going on?
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</A
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></DT
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><DT
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>4.1.12. <A
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HREF="lvm2faq.html#AEN401"
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> How are snapshots in LVM2 different from LVM1?
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</A
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></DT
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><DT
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>4.1.13. <A
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HREF="lvm2faq.html#AEN407"
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> What is the maximum size of a single LV?
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</A
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></DT
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></DL
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><DIV
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CLASS="qandaentry"
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><DIV
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CLASS="question"
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><P
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><A
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NAME="AEN279"
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></A
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><B
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>4.1.1. </B
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>
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I have LVM 1 installed and running on my system. How do
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I start using LVM 2?
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</P
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></DIV
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><DIV
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CLASS="answer"
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><P
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><B
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> </B
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>
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Here's the Quick Start instructions :)
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<P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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> Start by removing any snapshot LVs on the system.
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These are not handled by LVM 2 and will prevent the
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origin from being activated when LVM 2 comes up.
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</P
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></LI
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><LI
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><P
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> Make sure you have some way of booting the system
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other than from your standard boot partition. Have
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the LVM 1 tools, standard system tools (mount) and
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an LVM 1 compatible kernel on it in case you need to
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get back and fix some things.
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</P
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></LI
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><LI
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><P
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> Grab the LVM 2 tools source and the device mapper
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source and compile them. You need to install the
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device mapper library using <SPAN
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CLASS="QUOTE"
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>"make
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install"</SPAN
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> before compiling the LVM 2 tools.
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Also copy the dm/scripts/devmap_mknod.sh script into
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/sbin. I recommend only installing the 'lvm' binary
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for now so you have access to the LVM 1 tools if you
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need them. If you have access to packages for LVM 2
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and device-mapper, you can install those instead,
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but beware of them overwriting your LVM 1 tool set.
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</P
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></LI
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><LI
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><P
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> Get a device mapper compatible kernel, either built
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in or as a kernel module.
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</P
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></LI
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><LI
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><P
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> Figure out where LVM 1 was activated in your startup
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scripts. Make sure the device-mapper module is
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loaded by that point (if you are using device mapper
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as a module) and add '/sbin/devmap_mknod.sh; lvm
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vgscan; lvm vgchange -ay' afterward.
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</P
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></LI
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><LI
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><P
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> Install the kernel with device mapper support in it.
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Reboot. If all goes well, you should be running with
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lvm2.
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</P
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></LI
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></OL
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>
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</P
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></DIV
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></DIV
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><DIV
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CLASS="qandaentry"
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><DIV
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CLASS="question"
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><P
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><A
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NAME="AEN298"
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></A
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><B
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>4.1.2. </B
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>
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Do I need a special lvm2 kernel module?
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</P
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></DIV
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><DIV
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CLASS="answer"
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><P
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><B
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> </B
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>
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No. You need device-mapper. The lvm2 tools use
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device-mapper to interface with the kernel and do all
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their device mapping (hence the name device-mapper). As
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long as you have device-mapper, you should be able to
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use LVM2.
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</P
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></DIV
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></DIV
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><DIV
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CLASS="qandaentry"
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><DIV
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CLASS="question"
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><P
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><A
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NAME="AEN303"
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></A
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><B
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>4.1.3. </B
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>
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I get errors about
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<TT
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CLASS="filename"
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>/dev/mapper/control</TT
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> when I try to
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use the LVM 2 tools. What's going on?
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</P
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></DIV
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><DIV
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CLASS="answer"
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><P
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><B
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> </B
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>
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The primary cause of this is not having run the
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<SPAN
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CLASS="QUOTE"
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>"dmsetup mknodes"</SPAN
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> after rebooting into a dm
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capable kernel. This script generates the control node
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for device mapper.
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</P
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><P
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> If you don't have the <SPAN
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CLASS="QUOTE"
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>"dmsetup mknodes"</SPAN
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>,
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don't despair! (Though you should probably upgrade to
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the latest version of device-mapper.) It's pretty easy
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to create the <TT
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CLASS="filename"
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>/dev/mapper/control</TT
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>
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file on your own:
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<P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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> Make sure you have the device-mapper module loaded
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(if you didn't build it into your kernel).
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</P
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></LI
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><LI
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><P
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> Run
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="screen"
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># cat /proc/misc | grep device-mapper | awk '{print $1}'</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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and note the number
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printed. (If you don't get any output, refer to
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step 1.)
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</P
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></LI
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><LI
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><P
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> Run <TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="screen"
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># mkdir /dev/mapper</PRE
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></FONT
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></TD
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></TR
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></TABLE
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> - if you
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get an error saying
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<TT
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CLASS="filename"
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>/dev/mapper</TT
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> already exists,
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make sure it's a directory and move on.
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</P
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></LI
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><LI
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><P
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> Run
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="screen"
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># mknod /dev/mapper/control c 10 $number</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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where $number is the number printed in step 2.
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</P
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></LI
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></OL
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>
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You should be all set now!
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</P
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></DIV
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></DIV
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><DIV
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CLASS="qandaentry"
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><DIV
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CLASS="question"
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><P
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><A
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NAME="AEN326"
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></A
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><B
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>4.1.4. </B
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>
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Which commands and types of logical volumes are
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currently supported in LVM 2?
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</P
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></DIV
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><DIV
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CLASS="answer"
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><P
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><B
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> </B
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>
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If you are using the stable 2.4 device mapper patch from
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the lvm2 tarball, all the major functionality you'd
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expect using lvm1 is supported with the lvm2 tools.
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(You still need to remove snapshots before upgrading
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from lvm1 to lvm2)
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</P
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><P
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> If you are using the version of device mapper in the 2.6
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kernel.org kernel series the following commands and LV
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types are not supported:
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<P
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></P
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><UL
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><LI
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><P
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> pvmove </P
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></LI
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><LI
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><P
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> snapshots </P
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></LI
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></UL
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>
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The beginnings of support for these features are in the
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<A
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HREF="http://people.sistina.com/~thornber/dm/"
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TARGET="_top"
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> unstable device mapper patches</A
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> maintained by Joe
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Thornber.
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</P
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></DIV
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></DIV
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><DIV
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CLASS="qandaentry"
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><DIV
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|
CLASS="question"
|
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><P
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|
><A
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|
NAME="AEN338"
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></A
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|
><B
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|
>4.1.5. </B
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>
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Does LVM 2 use a different format from LVM 1 for it's
|
|
ondisk representation of Volume Groups and Logical
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Volumes?
|
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</P
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></DIV
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><DIV
|
|
CLASS="answer"
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><P
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><B
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> </B
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>
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Yes. LVM 2 uses lvm 2 format metadata. This format is much
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more flexible than the LVM 1 format metadata, removing
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or reducing most of the limitations LVM 1 had.
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</P
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></DIV
|
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></DIV
|
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><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN343"
|
|
></A
|
|
><B
|
|
>4.1.6. </B
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|
>
|
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Does LVM 2 support VGs and LVs created with LVM 1?
|
|
</P
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|
></DIV
|
|
><DIV
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|
CLASS="answer"
|
|
><P
|
|
><B
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|
> </B
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>
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Yes. LVM 2 will activate and operate on VG and LVs created
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with LVM 1. The exception to this is snapshots created with
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LVM 1 - these should be removed before upgrading. Snapshots
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that remain after upgrading will have to be removed before
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their origins can be activated by LVM 2.
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</P
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|
></DIV
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></DIV
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><DIV
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|
CLASS="qandaentry"
|
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><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN348"
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|
></A
|
|
><B
|
|
>4.1.7. </B
|
|
>
|
|
Can I upgrade my LVM 1 based VGs and LVs to LVM 2 native
|
|
format?
|
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</P
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|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
|
|
><B
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|
> </B
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>
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Yes. Use vgconvert to convert your VG and all LVs contained
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within it to the new lvm 2 format metadata. Be warned that it's
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not always possible to revert back to lvm 1 format metadata.
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|
</P
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|
></DIV
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></DIV
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|
><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN353"
|
|
></A
|
|
><B
|
|
>4.1.8. </B
|
|
>
|
|
I've upgraded to LVM 2, but the tools keep failing with out
|
|
of memory errors. What gives?
|
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</P
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|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
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|
><B
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|
> </B
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>
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One possible cause of this is that some versions of LVM
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|
1 (The user that reported this bug originally was using
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Mandrake 9.2, but it is not necessarily limited to that
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distribution) did not put a UUID into the PV and VG
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structures as they were supposed to. The most current
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versions of the LVM 2 tools automatically fill UUIDs in
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for the structures if they see they are missing, so you
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should grab a more current version and your problem
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should be solved. If not, post to the <A
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HREF="maillists.html"
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|
>linux-lvm mailing list</A
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>
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</P
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|
></DIV
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></DIV
|
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><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN359"
|
|
></A
|
|
><B
|
|
>4.1.9. </B
|
|
>
|
|
I have my root partition on an LV in LVM 1. How do I
|
|
upgrade to LVM 2? And what happened to lvmcreate_initrd?
|
|
</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
|
|
><B
|
|
> </B
|
|
>
|
|
Upgrading to LVM 2 is a bit trickier with root on LVM,
|
|
but it's not impossible. You need to queue up a kernel
|
|
with device-mapper support and install the lvm2 tools
|
|
(you might want to make a backup of the lvm 1 tools, or
|
|
find a rescue disk with the lvm tools built in, in case
|
|
you need them before you're done). Then find a mkinitrd
|
|
script that has support for your distro and lvm 2.
|
|
</P
|
|
><P
|
|
> Currently, this is the list of mkinitrd scripts that I
|
|
know support lvm2, sorted by distro:
|
|
<P
|
|
></P
|
|
><DIV
|
|
CLASS="variablelist"
|
|
><P
|
|
><B
|
|
>mkinitrd scripts with lvm 2 support</B
|
|
></P
|
|
><DL
|
|
><DT
|
|
>fedora</DT
|
|
><DD
|
|
><P
|
|
> The latest fedora core 2 <A
|
|
HREF="http://distro.ibiblio.org/pub/linux/distributions/fedora/linux/core/development/i386/Fedora/RPMS/mkinitrd-3.5.21-1.i386.rpm"
|
|
TARGET="_top"
|
|
>mkinitrd</A
|
|
>
|
|
handles lvm2, but it relies on a statically
|
|
built lvm binary from the latest lvm 2 tarball.
|
|
</P
|
|
><P
|
|
> Redhat 9 users may be able to use this as well
|
|
</P
|
|
></DD
|
|
><DT
|
|
>Debian</DT
|
|
><DD
|
|
><P
|
|
> There is an unofficial version <A
|
|
HREF="http://www.poochiereds.net/svn/lvm2/"
|
|
TARGET="_top"
|
|
>here</A
|
|
>
|
|
</P
|
|
></DD
|
|
><DT
|
|
>Generic</DT
|
|
><DD
|
|
><P
|
|
> There is a version in the lvm2 source tree under
|
|
<TT
|
|
CLASS="filename"
|
|
>scripts/lvm2_createinitrd/</TT
|
|
>.
|
|
See the documentation in that directory for more
|
|
details.
|
|
</P
|
|
></DD
|
|
></DL
|
|
></DIV
|
|
>
|
|
</P
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN383"
|
|
></A
|
|
><B
|
|
>4.1.10. </B
|
|
>
|
|
How resilient is LVM to a sudden renumbering of
|
|
physical hard disks?
|
|
</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
|
|
><B
|
|
> </B
|
|
>
|
|
It's fine - LVM identifies PVs by UUID, not by device
|
|
name.
|
|
</P
|
|
><P
|
|
> Each disk (PV) is labeled with a UUID, which uniquely
|
|
identifies it to the system. 'vgscan' identifies this
|
|
after a new disk is added that changes your drive
|
|
numbering. Most distros run vgscan in the lvm startup
|
|
scripts to cope with this on reboot after a hardware
|
|
addition. If you're doing a hot-add, you'll have to run
|
|
this by hand I think. On the other hand, if your vg is
|
|
activated and being used, the renumbering should not
|
|
affect it at all. It's only the activation that needs
|
|
the identifier, and the worst case scenario is that the
|
|
activation will fail without a vgscan with a complaint
|
|
about a missing PV.
|
|
</P
|
|
><DIV
|
|
CLASS="note"
|
|
><P
|
|
></P
|
|
><TABLE
|
|
CLASS="note"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="25"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><IMG
|
|
SRC="../images/note.gif"
|
|
HSPACE="5"
|
|
ALT="Note"></TD
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
><P
|
|
> The failure or removal of a drive that LVM is
|
|
currently using will cause problems with current use
|
|
and future activations of the VG that was using it.
|
|
</P
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN391"
|
|
></A
|
|
><B
|
|
>4.1.11. </B
|
|
>
|
|
I'm trying to fill my vg, and vgdisplay/vgs says that I
|
|
have 1.87 GB free, but when I do an lvcreate vg -L1.87G
|
|
it says "insufficient free extends". What's going on?
|
|
</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
|
|
><B
|
|
> </B
|
|
>
|
|
The 1.87 GB figure is rounded to 2 decimal places, so
|
|
it's probably 1.866 GB or something. This is a
|
|
human-readable output to give you a general idea of how
|
|
big the VG is. If you want to specify an exact size,
|
|
you must use extents instead of some multiple of bytes.
|
|
</P
|
|
><P
|
|
> In the case of vgdisplay, use the Free PE count instead
|
|
of the human readable capacity.
|
|
<TABLE
|
|
BORDER="0"
|
|
BGCOLOR="#E0E0E0"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
><FONT
|
|
COLOR="#000000"
|
|
><PRE
|
|
CLASS="screen"
|
|
> Free PE / Size 478 / 1.87 GB
|
|
^^^
|
|
</PRE
|
|
></FONT
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
>
|
|
So, this would indicate that you should do run
|
|
<TABLE
|
|
BORDER="0"
|
|
BGCOLOR="#E0E0E0"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
><FONT
|
|
COLOR="#000000"
|
|
><PRE
|
|
CLASS="screen"
|
|
> # lvcreate vg -l478 </PRE
|
|
></FONT
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
> Note that instead of an upper-case 'L',
|
|
we used a lower-case 'l' to tell lvm to use extents
|
|
instead of bytes.
|
|
</P
|
|
><P
|
|
> In the case of vgs, you need to instruct it to tell you how many extents are available:
|
|
<TABLE
|
|
BORDER="0"
|
|
BGCOLOR="#E0E0E0"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
><FONT
|
|
COLOR="#000000"
|
|
><PRE
|
|
CLASS="screen"
|
|
> # vgs -o +vg_free_count,vg_extent_count
|
|
</PRE
|
|
></FONT
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
>
|
|
This tell vgs to add the free extents and the total
|
|
number of extents to the end of the vgs listing. Use
|
|
the free extent number the same way you would in the
|
|
above vgdisplay case.
|
|
</P
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN401"
|
|
></A
|
|
><B
|
|
>4.1.12. </B
|
|
>
|
|
How are snapshots in LVM2 different from LVM1?
|
|
</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
|
|
><B
|
|
> </B
|
|
>
|
|
In LVM2 snapshots are read/write by default, whereas in
|
|
LVM1, snapshots were only read-only. See <A
|
|
HREF="snapshotintro.html"
|
|
>Section 3.8</A
|
|
> for more details
|
|
</P
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="qandaentry"
|
|
><DIV
|
|
CLASS="question"
|
|
><P
|
|
><A
|
|
NAME="AEN407"
|
|
></A
|
|
><B
|
|
>4.1.13. </B
|
|
>
|
|
What is the maximum size of a single LV?
|
|
</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="answer"
|
|
><P
|
|
><B
|
|
> </B
|
|
>
|
|
The answer to this question depends upon the CPU
|
|
architecture of your computer and the kernel you are a
|
|
running:
|
|
<P
|
|
></P
|
|
><UL
|
|
><LI
|
|
><P
|
|
> For 2.4 based kernels, the maximum LV size is 2TB.
|
|
For some older kernels, however, the limit was 1TB
|
|
due to signedness problems in the block layer.
|
|
Red Hat Enterprise Linux 3 Update 5 has fixes to
|
|
allow the full 2TB LVs. Consult your distribution
|
|
for more information in this regard.
|
|
</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
> For 32-bit CPUs on 2.6 kernels, the maximum LV size is 16TB.
|
|
</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
> For 64-bit CPUs on 2.6 kernels, the maximum LV
|
|
size is 8EB. (Yes, that is a very large number.)
|
|
</P
|
|
></LI
|
|
></UL
|
|
>
|
|
</P
|
|
></DIV
|
|
></DIV
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
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CLASS="NAVFOOTER"
|
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><HR
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ALIGN="LEFT"
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SUMMARY="Footer navigation table"
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|
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|
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|
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|
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|
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><A
|
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HREF="faq.html"
|
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ACCESSKEY="P"
|
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>Prev</A
|
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