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2003-03-08 Gregory Leblanc <gleblanc@linuxweasel.com> 

* Linux-RAID-FAQ.sgml: Removed, migrated to XML
	* Linux-RAID-FAQ.xml: Updated with new information.
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V3.1//EN">
<article class="faq" id="index">
<artheader>
<title>Linux-RAID FAQ</title>
<author>
<firstname>Gregory</firstname>
<surname>Leblanc</surname>
<affiliation>
<address>
<email>gleblanc (at) cu-portland.edu</email>
</address>
</affiliation>
</author>
<revhistory>
<revision>
<revnumber>v0.0.10</revnumber>
<date>24 April 2001</date>
<authorinitials>gml</authorinitials>
<revremark>
Added a new section and question about benchmarking.</revremark>
</revision>
<revision>
<revnumber>v0.0.9</revnumber>
<date>9 October 2000</date>
<authorinitials>gml</authorinitials>
<revremark>
Updates to the location of the patches, and a couple of other
things which I can't remember.</revremark>
</revision>
</revhistory>
<abstract>
<para>This is a FAQ for the Linux-RAID mailing list, hosted on
vger.kernel.org. vger.rutgers.edu is gone, so don't bother
looking for it. It's intended as a supplement to the existing
Linux-RAID HOWTO, to cover questions that keep occurring on the
mailing list. PLEASE read this document before your post to the
list.</para>
</abstract>
</artheader>
<qandaset>
<qandadiv>
<title>General</title>
<qandaentry>
<question>
<para>Where can I find archives for the linux-raid mailing
list?</para>
</question>
<answer>
<para>My favorite archives are at <ulink
url="http://www.geocrawler.com/lists/3/Linux/57/0/">http://www.geocrawler.com/lists/3/Linux/57/0/</ulink>.</para>
<para>Other archives are available at <ulink
url="http://marc.theaimsgroup.com/?l=linux-raid&amp;r=1&amp;w=2">http://marc.theaimsgroup.com/?l=linux-raid&amp;r=1&amp;w=2</ulink></para>
<para>Another archive site is <ulink
url="http://www.mail-archive.com/linux-raid@vger.rutgers.edu/">http://www.mail-archive.com/linux-raid@vger.rutgers.edu/</ulink></para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Where can I find the latest version of this FAQ?</para>
</question>
<answer>
<para>The latest version of this FAQ will be available from the
LDP website at <ulink
url="http://www.LinuxDoc.org/FAQ/">http://www.LinuxDoc.org/FAQ/</ulink>.
As soon as I get my server at home fixed I'll make it available
there as well.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What sorts of things does this list cover?</para>
</question>
<answer>
<para>Well, obviously this list covers RAID in relation to
Linux. Most of the discussions are related to the raid code
that's been built into the Linux kernel. There are also a few
discussions on getting hardware based RAID controllers working
using Linux as the operating system. Any and all of these
discussions are valid for this list.</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>Kernel</title>
<qandaentry>
<question>
<para>I'm running <replaceable>[insert your linux distribution
here]</replaceable>. Do I need to patch my kernel to make RAID
work?</para>
</question>
<answer>
<para>Well, the short answer is, it depends. Some distributions
are using the RAID 0.90 patches, while others leave the kernel
with the older md code. Unfortunately, I don't have a list of
which distributions have which kernels. If you'd like to
maintain such a list, please email me
&lt;<email>gleblanc@cu-portland.edu</email>&gt; as well as the
linux-raid mailing list.</para>
<para>
If you download a 2.2.x kernel from ftp.kernel.org, then you
will need to patch your kernel.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How can I tell if I need to patch my kernel?</para>
</question>
<answer>
<para>That depends on which kernel series you're using. If
you're using the 2.4.x kernels, then you've already got the
latest RAID code that's available. If you're running 2.2.x, see
the following instructions on how to find out.</para>
<para>The easiest way is to check what's in
<filename>/proc/mdstat</filename>. Here's a sample from a 2.2.x
kernel, <emphasis>with</emphasis> the RAID patches applied.
<screen format="linespecific">
[gleblanc@grego1 gleblanc]$ cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid5] [translucent]
read_ahead not set
unused devices: &lt;none&gt;
</screen>
If the contents of <filename>/proc/mdstat</filename> looks like the
above, then you don't need to patch your kernel.</para> <para>The
"Personalities" line in your kernel may not look exactly like the
above, if you have RAID compiled as modules. Most distributions
will have RAID compiled as modules to save space on the boot
diskette. If you're not using any RAID sets, then you will
probably see a blank space at the end of the "Personalities"
line, don't worry, that just means that the RAID modules aren't
loaded yet.</para>
<para>Here's a sample from a 2.2.x kernel,
<emphasis>without</emphasis> the RAID patches applied.
<screen format="linespecific">
[root@serek ~]# cat /proc/mdstat
Personalities : [1 linear] [2 raid0]
read_ahead not set
md0 : inactive
md1 : inactive
md2 : inactive
md3 : inactive
</screen>
<emphasis>If your <filename>/proc/mdstat</filename> looks like this
one, then you need to patch your kernel.</emphasis></para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Where can I get the latest RAID patches for my kernel?</para>
</question>
<answer>
<para>The patches for the 2.2.x kernels up to, and including,
2.2.13 are available from <ulink
url="ftp://ftp.kernel.org/pub/linux/daemons/raid/alpha/">ftp.kernel.org</ulink>.
Use the kernel patch that most closely matches your kernel
revision. For example, the 2.2.11 patch can also be used on
2.2.12 and 2.2.13.</para>
<para>The patches for 2.2.14 and later kernels are at <ulink
url="http://people.redhat.com/mingo/raid-patches/">http://people.redhat.com/mingo/raid-patches/</ulink>.
Use the right patch for your kernel, these patches haven't
worked on other kernel revisions yet. Please use something like
wget/curl/lftp to retrieve this patch, as it's easier on the
server than using a client like Netscape. Downloading patches
with Lynx has been unsuccessful for me; wget may be the easiest
way.
<note>
<para>These patches should also be available from
<ulink url="ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches/">
ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches/</ulink>
I could not find them on my local mirror, but please check
yours before using the main kernel.org site. You can find a
list of the local mirrors at <ulink
url="http://www.kernel.org/mirrors/">http://www.kernel.org/mirrors/</ulink>.</para>
</note>
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>How do I apply the patch to a kernel that I just
downloaded from ftp.kernel.org?</para>
</question>
<answer>
<para>First, unpack the kernel into some directory, generally
people use <filename class="directory">/usr/src/linux</filename>.
Change to this directory, and type <command>patch -p1 &lt;
/path/to/raid-version.patch</command>.
<informalexample>
<para>On my RedHat 6.2 system, I decompressed the 2.2.16 kernel
into <filename
class="directory">/usr/src/linux-2.2.16</filename>. From
<filename class="directory">/usr/src/linux-2.2.16</filename>, I
type in <command>patch -p1 &lt;
<replaceable>/home/gleblanc/raid-2.2.16-A0</replaceable></command>.
Then I rebuild the kernel using <command>make
menuconfig</command> and related builds.</para>
</informalexample>
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>What kind of drives can I use RAID with? Do only SCSI or
IDE drives work? Do I need different patches for different kinds
of drives?</para>
</question>
<answer>
<para>Software RAID works with any block device in the Linux
kernel. This includes IDE and SCSI drives, as well as most
harware RAID controllers. There are no different patches for IDE
drives vs. SCSI drives.</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>RAIDtools</title>
<qandaentry>
<question>
<para>Why are the RAIDtools at <ulink
url="http://people.redhat.com/mingo/raid-patches/">http://people.redhat.com/mingo/raid-patches/</ulink>
labeled <emphasis>dangerous</emphasis>, and if they're dangerous,
should I use them?</para>
</question>
<answer>
<para>The tools are labeled <emphasis>dangerous</emphasis>
because the RAID code isn't part of the <quote>stable</quote>
Linux kernel.</para> <para>The tools found at the above URL are
the latest and greatest. You <emphasis>should</emphasis> use
these tools with the kernel patches from the same
location.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Are there any tools other than the
<emphasis>dangerous</emphasis> ones available?</para>
</question>
<answer>
<para>No, the <emphasis>dangerous</emphasis> tools available from
<ulink
url="http://people.redhat.com/mingo/raid-patches/">http://people.redhat.com/mingo/raid-patches/</ulink>
are the most current tools to use. <emphasis>Everyone using
RAID with the patches at the above location should be using
these <emphasis>dangerous</emphasis> tools.</emphasis></para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>Disk Failures and Recovery</title>
<qandaentry>
<question>
<para>How can I tell if one of the disks in my RAID array has
failed?</para>
</question>
<answer>
<para>A couple of things should indicate when a disk has failed.
There should be quite a few messages in
<filename>/var/log/messages</filename> indicating errors
accessing that device, which should be a good indication that
something is wrong.</para> <para>You should also notice that your
<filename>/proc/mdstat</filename> looks different. Here's a snip
from a good /proc/mdstat
<screen format="linespecific">
[gleblanc@grego1 gleblanc]$ cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid5] [translucent]
read_ahead not set
md0 : active raid1 sdb5[0] sda5[1] 32000 blocks [2/2] [UU]
unused devices: &lt;none&gt;
</screen>
</para>
<para>And here's one from a <filename>/proc/mdstat</filename>
where one of the RAID sets has a missing disk.
<screen format="linespecific">
[gleblanc@grego1 gleblanc]$ cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid5] [translucent]
read_ahead not set
md0 : active raid1 sdb5[0] sda5[1] 32000 blocks [2/1] [U_]
unused devices: &lt;none&gt;
</screen>
</para>
<para>I don't know if <filename>/proc/mdstat</filename> will
reflect the status of a HOT SPARE. If you have set one up, you
should be watching <filename>/var/log/messages</filename> for any
disk failures. I'd like to get some logs of a disk failure, and
<filename>/proc/mdstat</filename> from a system with a hot
spare.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>So my RAID set is missing a disk, what do I do now?</para>
</question>
<answer>
<para>RAID generally doesn't mark a disk as bad unless it is, so
you probably need a new disk. Most disks have a 3 year warranty,
but some good SCSI hard drives may have a 5 year warranty. See
if you can get the manufacturer to replace the failed disk for
you.</para> <para>When you get the new disk, power down the
system, and install it, then partition the drive so that it has
partitions the size of your missing RAID partitions. After
you're finished partitioning the disk, use the command
<command>raidhotadd</command> to put the new disk into the array
and begin reconstruction. See <ulink
url="http://www.LinuxDoc.org/HOWTO/Software-RAID-HOWTO-6.html">Chapter
6</ulink> of the <ulink
url="http://www.LinuxDoc.org/HOWTO/Software-RAID-HOWTO.html">Software
RAID HOWTO</ulink> for more information.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para><command>dmesg</command> shows <quote>md: serializing
resync, md4 has overlapping physical units with md5</quote>.
What does this mean?</para>
</question>
<answer>
<para>In that message <quote>physical units</quote> refers to
disks, and not to blocks on the disks. Since there is more than
1 RAID array that needs resyncing on a disk, the RAID code is
going to sync md4 first, and md5 second, to avoid excessive seeks
(also called thrashing), which would drastically slow the resync
process.</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>Benchmarking</title>
<qandaentry>
<question>
<para>How should I benchmark my RAID devices? Are there any
tools that work particularly well?</para>
</question>
<answer>
<para>There are really a few options for benchmarking your RAID
array, depending on what you're looking to test. RAID offers the
greatest speed increases when there are multiple threads reading
from the same RAID volume.</para>
<para>One tool specificly designed to test and show off these
performance gains is <ulink
url="http://tiobench.sourceforge.net/"
type="http"><application>tiobench</application></ulink>. It uses
multiple read and write threads on the disk, and has some pretty
good reporting.</para>
<para>Another good tool to use is <ulink
url="http://www.coker.com.au/bonnie++/"
type="http"><application>bonnie++</application></ulink>. It
seems to be more targeted at benchmarking single drives that at
RAID, but still provides useful information.</para>
<para>One tool <emphasis>NOT</emphasis> to use is
<application>hdparm</application>. It does not give useful
performance numbers for any drives that I've heard about, and has
been known to give some incredibly off-the-wall numbers as well.
If you want to do <emphasis>real</emphasis> benchmarking, use
one of the tools listed above.</para>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</article>
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@ -1,22 +1,36 @@
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V3.1//EN">
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article class="faq" id="index">
<artheader>
<articleinfo>
<title>Linux-RAID FAQ</title>
<author>
<firstname>Gregory</firstname>
<surname>Leblanc</surname>
<affiliation>
<address>
<email>gleblanc (at) cu-portland.edu</email>
</address>
</affiliation>
<email>gleblanc@linuxweasel.com</email>
</author>
<revhistory>
<revision>
<revnumber>v0.0.12</revnumber>
<date>2003-03-05</date>
<authorinitials>gml</authorinitials>
<revremark>Fleshed out questions that cover using mdadm, small formatting
changes</revremark>
</revision>
<revision>
<revnumber>v0.0.11</revnumber>
<date>2003-01-08</date>
<authorinitials>gml</authorinitials>
<revremark>Updated Archive Locations, information on when to patch, added
a note about old patches being missing, removed question about the
raidtools being dangerous (since they don't appear to be so labeled any
longer). </revremark>
</revision>
<revision>
<revnumber>v0.0.10</revnumber>
<date>24 April 2001</date>
@ -25,15 +39,6 @@
Added a new section and question about benchmarking.</revremark>
</revision>
<revision>
<revnumber>v0.0.9</revnumber>
<date>9 October 2000</date>
<authorinitials>gml</authorinitials>
<revremark>
Updates to the location of the patches, and a couple of other
things which I can't remember.</revremark>
</revision>
</revhistory>
@ -47,29 +52,71 @@
</abstract>
</artheader>
<legalnotice>
<qandaset>
<title>Linux RAID FAQ Copyright</title>
<qandadiv>
<title>General</title>
<para>This documentation was developed for the Linux Documentation Project
by Gregory Leblanc.</para>
<qandaentry>
<question>
<para>Redistribution and use in source (XML DocBook) and 'compiled' forms
(XML, HTML, PDF, PostScript, RTF and so forth) with or without
modification, are permitted provided that the following conditions are
met:</para>
<orderedlist>
<listitem>
<para>Redistributions of source code (XML DocBook) must
retain the above copyright notice, this list of conditions
and the following disclaimer as the first lines of this file
unmodified.</para>
</listitem>
<listitem>
<para>Redistributions in compiled form (transformed to other
DTDs, converted to PDF, PostScript, RTF and other formats)
must reproduce the above copyright notice, this list of
conditions and the following disclaimer in the documentation
and/or other materials provided with the
distribution.</para>
</listitem>
</orderedlist>
<important>
<para>THIS DOCUMENTATION IS PROVIDED BY THE GREGORY LEBLANC "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NETWORKS ASSOCIATES
TECHNOLOGY, INC BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
DOCUMENTATION, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.</para>
</important>
</legalnotice>
</articleinfo>
<qandaset>
<qandadiv id="general">
<title>General</title>
<qandaentry id="archives">
<question>
<para>Where can I find archives for the linux-raid mailing
list?</para>
</question>
<answer>
<para>My favorite archives are at <ulink
url="http://www.geocrawler.com/lists/3/Linux/57/0/">http://www.geocrawler.com/lists/3/Linux/57/0/</ulink>.</para>
<para>Other archives are available at <ulink
<para>The only archives left seem to be available at <ulink
url="http://marc.theaimsgroup.com/?l=linux-raid&amp;r=1&amp;w=2">http://marc.theaimsgroup.com/?l=linux-raid&amp;r=1&amp;w=2</ulink></para>
<para>Another archive site is <ulink
url="http://www.mail-archive.com/linux-raid@vger.rutgers.edu/">http://www.mail-archive.com/linux-raid@vger.rutgers.edu/</ulink></para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="wherefaq">
<question>
<para>Where can I find the latest version of this FAQ?</para>
</question>
@ -77,14 +124,12 @@
<answer>
<para>The latest version of this FAQ will be available from the
LDP website at <ulink
url="http://www.LinuxDoc.org/FAQ/">http://www.LinuxDoc.org/FAQ/</ulink>.
As soon as I get my server at home fixed I'll make it available
there as well.</para>
url="http://www.tldp.org/FAQ/">http://www.tldp.org/FAQ/</ulink>.</para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="listcovers">
<question>
<para>What sorts of things does this list cover?</para>
</question>
@ -102,12 +147,10 @@
</qandadiv>
<qandadiv>
<qandadiv id="kernel">
<title>Kernel</title>
<qandaentry>
<qandaentry id="whoneedstopatch">
<question>
<para>I'm running <replaceable>[insert your linux distribution
here]</replaceable>. Do I need to patch my kernel to make RAID
@ -115,21 +158,16 @@
</question>
<answer>
<para>Well, the short answer is, it depends. Some distributions
are using the RAID 0.90 patches, while others leave the kernel
with the older md code. Unfortunately, I don't have a list of
which distributions have which kernels. If you'd like to
maintain such a list, please email me
&lt;<email>gleblanc@cu-portland.edu</email>&gt; as well as the
linux-raid mailing list.</para>
<para>At this point, most major distributions are shipping with a 2.4
based kernel, which already includes the necessary patches. If your
distribution is still using a 2.2.x kernel, upgrade!</para>
<para>
If you download a 2.2.x kernel from ftp.kernel.org, then you
will need to patch your kernel.</para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="needtopatch">
<question>
<para>How can I tell if I need to patch my kernel?</para>
</question>
@ -179,13 +217,10 @@ md3 : inactive
<emphasis>If your <filename>/proc/mdstat</filename> looks like this
one, then you need to patch your kernel.</emphasis></para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="wherepatches">
<question>
<para>Where can I get the latest RAID patches for my kernel?</para>
</question>
@ -196,46 +231,37 @@ one, then you need to patch your kernel.</emphasis></para>
url="ftp://ftp.kernel.org/pub/linux/daemons/raid/alpha/">ftp.kernel.org</ulink>.
Use the kernel patch that most closely matches your kernel
revision. For example, the 2.2.11 patch can also be used on
2.2.12 and 2.2.13.</para>
2.2.12 and 2.2.13. <important>
<para>These patches are no longer available
from this location! I haven't been able to find the new location for
them, please email me if you know where they've gone.</para>
</important>
</para>
<para>The patches for 2.2.14 and later kernels are at <ulink
url="http://people.redhat.com/mingo/raid-patches/">http://people.redhat.com/mingo/raid-patches/</ulink>.
Use the right patch for your kernel, these patches haven't
worked on other kernel revisions yet. Please use something like
worked on other kernel revisions. Please use something like
wget/curl/lftp to retrieve this patch, as it's easier on the
server than using a client like Netscape. Downloading patches
with Lynx has been unsuccessful for me; wget may be the easiest
way.
<note>
<para>These patches should also be available from
<ulink url="ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches/">
ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches/</ulink>
I could not find them on my local mirror, but please check
yours before using the main kernel.org site. You can find a
list of the local mirrors at <ulink
url="http://www.kernel.org/mirrors/">http://www.kernel.org/mirrors/</ulink>.</para>
</note>
</para>
way.</para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="howtopatch">
<question>
<para>How do I apply the patch to a kernel that I just
downloaded from ftp.kernel.org?</para>
</question>
<answer>
<para>First, unpack the kernel into some directory, generally
people use <filename class="directory">/usr/src/linux</filename>.
Change to this directory, and type <command>patch -p1 &lt;
/path/to/raid-version.patch</command>.
<informalexample>
<para>On my RedHat 6.2 system, I decompressed the 2.2.16 kernel
into <filename
class="directory">/usr/src/linux-2.2.16</filename>. From
@ -247,13 +273,10 @@ one, then you need to patch your kernel.</emphasis></para>
</informalexample>
</para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="whichdrives">
<question>
<para>What kind of drives can I use RAID with? Do only SCSI or
IDE drives work? Do I need different patches for different kinds
@ -270,54 +293,45 @@ one, then you need to patch your kernel.</emphasis></para>
</qandadiv>
<qandadiv>
<title>RAIDtools</title>
<qandadiv id="tools">
<title>RAID tools</title>
<qandaentry>
<qandaentry id="whattools">
<question>
<para>Why are the RAIDtools at <ulink
url="http://people.redhat.com/mingo/raid-patches/">http://people.redhat.com/mingo/raid-patches/</ulink>
labeled <emphasis>dangerous</emphasis>, and if they're dangerous,
should I use them?</para>
<para>What tools are available for dealing with my Linux Software RAID
arrays?</para>
</question>
<answer>
<para>The tools are labeled <emphasis>dangerous</emphasis>
because the RAID code isn't part of the <quote>stable</quote>
Linux kernel.</para> <para>The tools found at the above URL are
the latest and greatest. You <emphasis>should</emphasis> use
these tools with the kernel patches from the same
location.</para>
<para>There are currently two sets of tools available. Both sets work
quite well, and have essentially the same functionalty. I recommend the
newer set of tools, because they're much easier to use, but I'll mention
where to get the older tools as well.</para>
<para>The new set of tools is called <application>mdadm</application>.
It doesn't have much of a homepage, but you can download tarballs and
RPMs from <ulink
url="http://www.cse.unsw.edu.au/~neilb/source/mdadm/">http://www.cse.unsw.edu.au/~neilb/source/mdadm/</ulink>.
I suggest that anyone who isn't already familar with the 'raidtools'
package use these (and in fact, I suggest that folks who already know the
raidtools package switch over to these).</para>
<para>The older set of tools is called
<application>raidtools</application>. They're available from <ulink
url="http://people.redhat.com/mingo/raidtools/">http://people.redhat.com/mingo/raidtools/</ulink>.
I believe there are other locations available, since Red Hat Linux is
shipping based on a tarball numbered 1.00.3, which I can't find online.
If anybody knows where these are, please let me know.</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>Are there any tools other than the
<emphasis>dangerous</emphasis> ones available?</para>
</question>
<answer>
<para>No, the <emphasis>dangerous</emphasis> tools available from
<ulink
url="http://people.redhat.com/mingo/raid-patches/">http://people.redhat.com/mingo/raid-patches/</ulink>
are the most current tools to use. <emphasis>Everyone using
RAID with the patches at the above location should be using
these <emphasis>dangerous</emphasis> tools.</emphasis></para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<qandadiv id="failrecover">
<title>Disk Failures and Recovery</title>
<qandaentry>
<qandaentry id="hasfailed">
<question>
<para>How can I tell if one of the disks in my RAID array has
failed?</para>
@ -365,58 +379,69 @@ unused devices: &lt;none&gt;
</qandaentry>
<qandaentry>
<qandaentry id="missingdisk">
<question>
<para>So my RAID set is missing a disk, what do I do now?</para>
</question>
<answer>
<para>RAID generally doesn't mark a disk as bad unless it is, so
you probably need a new disk. Most disks have a 3 year warranty,
but some good SCSI hard drives may have a 5 year warranty. See
if you can get the manufacturer to replace the failed disk for
you.</para> <para>When you get the new disk, power down the
system, and install it, then partition the drive so that it has
partitions the size of your missing RAID partitions. After
you're finished partitioning the disk, use the command
<command>raidhotadd</command> to put the new disk into the array
and begin reconstruction. See <ulink
<para>Software-RAID generally doesn't mark a disk as bad unless it is, so
you probably need a new disk. Most decent quality disks have a 3 year
warranty, but some exceptional (and expensive) SCSI hard drives may have
wararnties as long as 5 years, or even longer. More and more hard drive
vendors are giving a 1 year warranty on their "consumer" drives. I
suggest avoiding any drive with a 1 year warranty if at all possible.
Try to have the manufacturer replace the failed disk if it's still under
warranty.</para>
<para>When you get the new disk, power down the system, and install it,
then partition the drive so that it has partitions the size of your
missing RAID partitions. Once you have the partitions set up properly,
just run <command>mdadm --add <replaceable>/dev/md0</replaceable>
<replaceable>/dev/hdc1</replaceable></command>, where
<replaceable>/dev/md0</replaceable> is the RAID array you're adding the
partition to, and <replaceable>/dev/hdc1</replaceable> is the partition
that you're trying to add. Reconstruction should start
immediately.</para>
<para>If you would prefer to use the RAIDtools suite, you can use the
command <command>raidhotadd</command> to put the new disk into the array
and begin reconstruction. See <ulink
url="http://www.LinuxDoc.org/HOWTO/Software-RAID-HOWTO-6.html">Chapter
6</ulink> of the <ulink
url="http://www.LinuxDoc.org/HOWTO/Software-RAID-HOWTO.html">Software
RAID HOWTO</ulink> for more information.</para>
</answer>
</qandaentry>
<qandaentry>
<qandaentry id="overlap">
<question>
<para><command>dmesg</command> shows <quote>md: serializing
resync, md4 has overlapping physical units with md5</quote>.
What does this mean?</para>
<para><command>dmesg</command> shows <quote>md: serializing resync,
<replaceable>md4</replaceable> has overlapping physical units
with <replaceable>md5</replaceable></quote> (where md4 and md5 are two
of your software RAID devices). What does this mean?</para>
</question>
<answer>
<para>In that message <quote>physical units</quote> refers to
disks, and not to blocks on the disks. Since there is more than
1 RAID array that needs resyncing on a disk, the RAID code is
going to sync md4 first, and md5 second, to avoid excessive seeks
(also called thrashing), which would drastically slow the resync
process.</para>
one RAID array that needs resyncing on one of the disks in use for your
RAID arrays, the RAID code is going to sync md4 first, and md5 second, to
avoid excessive seeks (also called thrashing), which would drastically
slow the resync process.</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<qandadiv id="benchmarking">
<title>Benchmarking</title>
<qandaentry>
<qandaentry id="howbenchmark">
<question>
<para>How should I benchmark my RAID devices? Are there any
tools that work particularly well?</para>
@ -447,9 +472,7 @@ unused devices: &lt;none&gt;
been known to give some incredibly off-the-wall numbers as well.
If you want to do <emphasis>real</emphasis> benchmarking, use
one of the tools listed above.</para>
</answer>
</qandaentry>
</qandadiv>
@ -461,7 +484,7 @@ unused devices: &lt;none&gt;
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