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Subject: ANNOUNCE: mdadm 3.0-devel1 - A tool for managing Soft RAID under Linux
I am pleased to announce the availability of
mdadm version 3.0-devel1
It is available at the usual places:
countrycode=xx.
http://www.${countrycode}kernel.org/pub/linux/utils/raid/mdadm/
and via git at
git://neil.brown.name/mdadm
http://neil.brown.name/git?p=mdadm
Note that this is a "devel" release. It is not intended for
production use yet, but rather for testing and ongoing development.
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.
The manual pages have not yet been updated, but here is a brief outline.
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]
The 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.
Any testing and feedback will be greatly appreciated.
NeilBrown 18th September 2008
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