1 Subject: ANNOUNCE: mdadm 3.0-rc1 - A tool for managing Soft RAID under Linux
3 I am pleased to announce the availability of
6 It is available at the usual places:
8 http://www.${countrycode}kernel.org/pub/linux/utils/raid/mdadm/
10 git://neil.brown.name/mdadm
11 http://neil.brown.name/git?p=mdadm
13 This is a "release candidate" which means that I think it is safe
14 to use and that there will be no significant change in functionality
17 The man pages aren't really "release candidate" yet but I will be
18 working on them before the final release.
20 The most significant changes since -devel3 relate to the names of md
21 devices as they appear in /dev and /dev/md/, and in particular the names
22 that are used when an array is assembled with "--incremental" or with
23 "mdadm --assemble --scan" when there are no ARRAY lines in mdadm.conf.
24 In these cases mdadm needs to deduce a name to use, and to try to
25 avoid using a name that a different array might have a stronger claim to.
27 - if the array is mentioned in mdadm.conf, use the name given there.
28 - if the array appear to have been created for "this host" using the
29 "homehost" concept, trust the name given in the metadata
30 - if the new setting "HOMEHOST <ignore>" is given (can be in mdadm.conf
31 or on command line) the the name given in the metadata is not
32 associated with some other array by mdadm.conf, then trust the
33 name given in the metadata
34 - otherwise use the name in the metadata, but in an untrusted manner.
36 If a name is untrusted, or if the name is already in use by another
37 array, then a numeric suffix like "_0", "_1" is appended to create
38 a unique name for the array.
40 That name is then used to create a device file in /dev/md/.
42 So if all arrays needed for boot will always be listed in
43 /etc/mdadm.conf, then it is appropriate to add "HOMEHOST <ignore>" to
44 mdadm.conf and there is no risk of conflicting names. However if you
45 want auto-assemble to assemble all arrays at boot time and you don't
46 want to list them in mdadm.conf, then don't give "HOMEHOST <ignore>"
47 either else there could be a risk of the wrong array being assembled
52 The following is the same introduction to 3.x as appeared in
53 previous announcements.
55 Any testing and feedback will be greatly appreciated.
57 NeilBrown 11th May 2009
60 =====================================================
62 The significant change which justifies the new major version number is
63 that mdadm can now handle metadata updates entirely in userspace.
64 This allows mdadm to support metadata formats that the kernel knows
67 Currently two such metadata formats are supported:
68 - DDF - The SNIA standard format
69 - Intel Matrix - The metadata used by recent Intel ICH controlers.
71 Also the approach to device names has changed significantly.
73 If udev is installed on the system, mdadm will not create any devices
74 in /dev. Rather it allows udev to manage those devices. For this to work
75 as expected, the included udev rules file should be installed.
77 If udev is not install, mdadm will still create devices and symlinks
78 as required, and will also remove them when the array is stopped.
80 mdadm now requires all devices which do not have a standard name (mdX
81 or md_dX) to live in the directory /dev/md/. Names in this directory
82 will always be created as symlinks back to the standard name in /dev.
84 The man pages contain some information about the new externally managed
85 metadata. However see below for a more condensed overview.
87 Externally managed metadata introduces the concept of a 'container'.
88 A container is a collection of (normally) physical devices which have
89 a common set of metadata. A container is assembled as an md array, but
92 A container can contain one or more data arrays. These are composed from
93 slices (partitions?) of various devices in the container.
95 For example, a 5 devices DDF set can container a RAID1 using the first
96 half of two devices, a RAID0 using the first half of the remain 3 devices,
97 and a RAID5 over thte second half of all 5 devices.
99 A container can be created with
101 mdadm --create /dev/md0 -e ddf -n5 /dev/sd[abcde]
103 or "-e imsm" to use the Intel Matrix Storage Manager.
105 An array can be created within a container either by giving the
106 container name and the only member:
108 mdadm -C /dev/md1 --level raid1 -n 2 /dev/md0
110 or by listing the component devices
112 mdadm -C /dev/md2 --level raid0 -n 3 /dev/sd[cde]
114 To assemble a container, it is easiest just to pass each device in turn to
117 for i in /dev/sd[abcde]
121 This will assemble the container and the components.
123 Alternately the container can be assembled explicitly
125 mdadm -A /dev/md0 /dev/sd[abcde]
127 Then the components can all be assembled with
131 For each container, mdadm will start a program called "mdmon" which will
132 monitor the array and effect any metadata updates needed. The array is
133 initially assembled readonly. It is up to "mdmon" to mark the metadata
134 as 'dirty' and which the array to 'read-write'.
136 The version 0.90 and 1.x metadata formats supported by previous
137 versions for mdadm are still supported and the kernel still performs
138 the same updates it use to. The new 'mdmon' approach is only used for
139 newly introduced metadata types.