mdadm resource

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Use the mdadm resource to manage RAID devices in a Linux environment using the mdadm utility. The mdadm resource will create and assemble an array, but it will not create the config file that is used to persist the array upon reboot. If the config file is required, it must be done by specifying a template with the correct array layout, and then by using the mount resource to create a file systems table (fstab) entry.

Syntax

The mdadm resource has the following syntax:

mdadm 'name' do
  bitmap           String
  chunk            Integer # default value: 16
  devices          Array
  layout           String
  level            Integer # default value: 1
  metadata         String # default value: "0.90"
  raid_device      String # default value: 'name' unless specified
  action           Symbol # defaults to :create if not specified
end

where:

  • mdadm is the resource.
  • name is the name given to the resource block.
  • action identifies which steps the chef-client will take to bring the node into the desired state.
  • bitmap, chunk, devices, layout, level, metadata, and raid_device are the properties available to this resource.

Actions

The mdadm resource has the following actions:

:assemble
Assemble a previously created array into an active array.
:create
Default. Create an array with per-device superblocks. If an array already exists (but does not match), update that array to match.
:nothing
This resource block does not act unless notified by another resource to take action. Once notified, this resource block either runs immediately or is queued up to run at the end of the Chef Client run.
:stop
Stop an active array.

Properties

The mdadm resource has the following properties:

bitmap

Ruby Type: String

The path to a file in which a write-intent bitmap is stored.

chunk

Ruby Type: Integer | Default Value: 16

The chunk size. This property should not be used for a RAID 1 mirrored pair (i.e. when the level property is set to 1).

devices

Ruby Type: Array

The devices to be part of a RAID array.

layout

Ruby Type: String

The RAID5 parity algorithm. Possible values: left-asymmetric (or la), left-symmetric (or ls), right-asymmetric (or ra), or right-symmetric (or rs).

level

Ruby Type: Integer | Default Value: 1

The RAID level.

metadata

Ruby Type: String | Default Value: "0.90"

The superblock type for RAID metadata.

raid_device

Ruby Type: String | Default Value: The resource block's name

Optional property to specify the name of the RAID device if it differs from the resource block’s name.

Common Resource Functionality

Chef resources include common properties, notifications, and resource guards.

Common Properties

The following properties are common to every resource:

ignore_failure

Ruby Type: true, false | Default Value: false

Continue running a recipe if a resource fails for any reason.

retries

Ruby Type: Integer | Default Value: 0

The number of attempts to catch exceptions and retry the resource.

retry_delay

Ruby Type: Integer | Default Value: 2

The retry delay (in seconds).

sensitive

Ruby Type: true, false | Default Value: false

Ensure that sensitive resource data is not logged by the chef-client.

Notifications

notifies

Ruby Type: Symbol, ‘Chef::Resource[String]’

A resource may notify another resource to take action when its state changes. Specify a 'resource[name]', the :action that resource should take, and then the :timer for that action. A resource may notify more than one resource; use a notifies statement for each resource to be notified.

A timer specifies the point during the Chef Client run at which a notification is run. The following timers are available:

:before
Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.
:delayed
Default. Specifies that a notification should be queued up, and then executed at the end of the Chef Client run.
:immediate, :immediately
Specifies that a notification should be run immediately, per resource notified.

The syntax for notifies is:

notifies :action, 'resource[name]', :timer
subscribes
Ruby Type: Symbol, ‘Chef::Resource[String]’

A resource may listen to another resource, and then take action if the state of the resource being listened to changes. Specify a 'resource[name]', the :action to be taken, and then the :timer for that action.

Note that subscribes does not apply the specified action to the resource that it listens to - for example:

file '/etc/nginx/ssl/example.crt' do
  mode '0600'
  owner 'root'
end

service 'nginx' do
  subscribes :reload, 'file[/etc/nginx/ssl/example.crt]', :immediately
end

In this case the subscribes property reloads the nginx service whenever its certificate file, located under /etc/nginx/ssl/example.crt, is updated. subscribes does not make any changes to the certificate file itself, it merely listens for a change to the file, and executes the :reload action for its resource (in this example nginx) when a change is detected.

A timer specifies the point during the Chef Client run at which a notification is run. The following timers are available:

:before
Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.
:delayed
Default. Specifies that a notification should be queued up, and then executed at the end of the Chef Client run.
:immediate, :immediately
Specifies that a notification should be run immediately, per resource notified.

The syntax for subscribes is:

subscribes :action, 'resource[name]', :timer

Guards

A guard property can be used to evaluate the state of a node during the execution phase of the chef-client run. Based on the results of this evaluation, a guard property is then used to tell the chef-client if it should continue executing a resource. A guard property accepts either a string value or a Ruby block value:

  • A string is executed as a shell command. If the command returns 0, the guard is applied. If the command returns any other value, then the guard property is not applied. String guards in a powershell_script run Windows PowerShell commands and may return true in addition to 0.
  • A block is executed as Ruby code that must return either true or false. If the block returns true, the guard property is applied. If the block returns false, the guard property is not applied.

A guard property is useful for ensuring that a resource is idempotent by allowing that resource to test for the desired state as it is being executed, and then if the desired state is present, for the chef-client to do nothing.

The following properties can be used to define a guard that is evaluated during the execution phase of the chef-client run:

not_if
Prevent a resource from executing when the condition returns true.
only_if
Allow a resource to execute only if the condition returns true.

Examples

The following examples demonstrate various approaches for using resources in recipes:

Create and assemble a RAID 0 array

The mdadm command can be used to create RAID arrays. For example, a RAID 0 array named /dev/md0 with 10 devices would have a command similar to the following:

$ mdadm --create /dev/md0 --level=0 --raid-devices=10 /dev/s01.../dev/s10

where /dev/s01 .. /dev/s10 represents 10 devices (01, 02, 03, and so on). This same command, when expressed as a recipe using the mdadm resource, would be similar to:

mdadm '/dev/md0' do
  devices [ '/dev/s01', ... '/dev/s10' ]
  level 0
  action :create
end

(again, where /dev/s01 .. /dev/s10 represents devices /dev/s01, /dev/s02, /dev/s03, and so on).

Create and assemble a RAID 1 array

mdadm '/dev/md0' do
  devices [ '/dev/sda', '/dev/sdb' ]
  level 1
  action [ :create, :assemble ]
end

Create and assemble a RAID 5 array

The mdadm command can be used to create RAID arrays. For example, a RAID 5 array named /dev/sd0 with 4, and a superblock type of 0.90 would be similar to:

mdadm '/dev/sd0' do
  devices [ '/dev/s1', '/dev/s2', '/dev/s3', '/dev/s4' ]
  level 5
  metadata '0.90'
  chunk 32
  action :create
end