atom feed16 messages in org.kernel.vger.linux-raidANNOUNCE: mdadm 3.0 - A tool for mana...
FromSent OnAttachments
Neil BrownJun 1, 2009 10:50 pm 
Jeff GarzikJun 2, 2009 1:11 pm 
Dan WilliamsJun 2, 2009 3:58 pm 
Neil BrownJun 2, 2009 8:56 pm 
Anton AltaparmakovJun 3, 2009 6:01 am 
Heinz MauelshagenJun 3, 2009 7:42 am 
Dan WilliamsJun 3, 2009 10:26 am 
Neil BrownJun 3, 2009 3:59 pm 
Mr. James W. LaferriereJun 3, 2009 6:52 pm 
Neil BrownJun 3, 2009 7:30 pm 
Anton AltaparmakovJun 4, 2009 2:00 am 
Heinz MauelshagenJun 4, 2009 9:38 am 
Bill DavidsenJun 6, 2009 4:15 pm 
Neil BrownJun 8, 2009 4:32 pm 
Neil BrownJun 8, 2009 4:35 pm 
Heinz MauelshagenJun 9, 2009 9:29 am 
Subject:ANNOUNCE: mdadm 3.0 - A tool for managing Soft RAID under Linux
From:Neil Brown (
Date:Jun 1, 2009 10:50:33 pm

I am pleased to (finally) announce the availability of mdadm version 3.0

It is available at the usual places: countrycode=xx. http://www.${countrycode} and via git at git://

This is a major new version and as such should be treated with some caution. However it has seen substantial testing and is considerred to be ready for wide use.

The significant change which justifies the new major version number is that mdadm can now handle metadata updates entirely in userspace. This allows mdadm to support metadata formats that the kernel knows nothing about.

Currently two such metadata formats are supported: - DDF - The SNIA standard format - Intel Matrix - The metadata used by recent Intel ICH controlers.

Also the approach to device names has changed significantly.

If udev is installed on the system, mdadm will not create any devices in /dev. Rather it allows udev to manage those devices. For this to work as expected, the included udev rules file should be installed.

If udev is not installed, mdadm will still create devices and symlinks as required, and will also remove them when the array is stopped.

mdadm now requires all devices which do not have a standard name (mdX or md_dX) to live in the directory /dev/md/. Names in this directory will always be created as symlinks back to the standard name in /dev.

The man pages contain some information about the new externally managed metadata. However see below for a more condensed overview.

Externally managed metadata introduces the concept of a 'container'. A container is a collection of (normally) physical devices which have a common set of metadata. A container is assembled as an md array, but is left 'inactive'.

A container can contain one or more data arrays. These are composed from slices (partitions?) of various devices in the container.

For example, a 5 devices DDF set can container a RAID1 using the first half of two devices, a RAID0 using the first half of the remain 3 devices, and a RAID5 over thte second half of all 5 devices.

A container can be created with

mdadm --create /dev/md0 -e ddf -n5 /dev/sd[abcde]

or "-e imsm" to use the Intel Matrix Storage Manager.

An array can be created within a container either by giving the container name and the only member:

mdadm -C /dev/md1 --level raid1 -n 2 /dev/md0

or by listing the component devices

mdadm -C /dev/md2 --level raid0 -n 3 /dev/sd[cde]

To assemble a container, it is easiest just to pass each device in turn to mdadm -I

for i in /dev/sd[abcde] do mdadm -I $i done

This will assemble the container and the components.

Alternately the container can be assembled explicitly

mdadm -A /dev/md0 /dev/sd[abcde]

Then the components can all be assembled with

mdadm -I /dev/md0

For each container, mdadm will start a program called "mdmon" which will monitor the array and effect any metadata updates needed. The array is initially assembled readonly. It is up to "mdmon" to mark the metadata as 'dirty' and which the array to 'read-write'.

The version 0.90 and 1.x metadata formats supported by previous versions for mdadm are still supported and the kernel still performs the same updates it use to. The new 'mdmon' approach is only used for newly introduced metadata types.

NeilBrown 2nd June 2009