DDF Fake RAID

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The last requirement is optional, but not having it means to have to modify the system after installation to use '''mdadm''' instead of '''dmraid''', and that is an expert task.
 
The last requirement is optional, but not having it means to have to modify the system after installation to use '''mdadm''' instead of '''dmraid''', and that is an expert task.
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= mdadm on DDF fake RAID for various distributions =
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This is work in progress. I will describe the installation procedure for some distributions, hoping that users of other distributions will follow up.
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== RHEL 6 / CentOS 6 ==
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 +
'''This description is not complete yet!!!'''
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 +
You need to download the source RPM of mdadm. Use [[File:mdadm.spec.txt]] as a replacement for the spec file.

Revision as of 19:01, 18 August 2013

Contents

Enabling MD RAID on DDF Fake / BIOS RAID systems

The terms "Fake RAID" or "BIOS RAID" denote systems with no RAID controller, but with a simple BIOS that is able to do basic RAID operations on an array of disks. For the actual runtime RAID implementation, this RAID solution relies on a OS driver. On Windows this will usually be a driver from the RAID vendor. On Linux, the MD RAID stack can be used as a fully featured, well tested and stable RAID stack - if mdadm understands the meta data used by the vendor. Linux has another tool as well, dmraid, which uses the kernel device mapper to access the data on the RAID arrays, but doesn't qualify as a fully featured RAID solution to the same extent as MD/mdadm. The advantage of dmraid over mdadm is that it understands many more meta data formats. As of 2013, most distributions use dmraid to access fake RAID in any format except the Intel IMSM (also "ISW", "Matrix") format.

One meta data format commonly found on modern RAID systems (real as well as "fake" RAID) is the SNIA DDF format. Both mdadm and dmraid have supported it for some time. This page is about tweaking Linux distributions to use mdadm rather than dmraid for DDF.

General Requirements

In order to run a DDF disk array with MD, your distribution needs

  1. a recent version of mdadm. As of 2013/08, I recommend a pre-release of mdadm 3.3. DDF support in mdadm has seen a lot of fixes and improvements in 3.3;
  2. udev rules that support invoking mdadm (rather than dmraid) when disks with DDF meta data are detected;
  3. support for mdadm on DDF in initial RAM disk, i.e. in tools like mkinitrd or dracut;
  4. support for mdadm on DDF in the OS installer.

The last requirement is optional, but not having it means to have to modify the system after installation to use mdadm instead of dmraid, and that is an expert task.

mdadm on DDF fake RAID for various distributions

This is work in progress. I will describe the installation procedure for some distributions, hoping that users of other distributions will follow up.

RHEL 6 / CentOS 6

This description is not complete yet!!!

You need to download the source RPM of mdadm. Use File:Mdadm.spec.txt as a replacement for the spec file.

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