Device identification

On modern Linux, block devices can be identified in number of ways. Some of them are stable across reboots, some other are nice to remeber and it is also possible to configure block device names using udev rules.

For example, all these paths refer to the same block device:

• /dev/disk/by-id/ata-Samsung_SSD_840_Series_S19MNSAD500335K
• /dev/disk/by-id/wwn-0x50025385a0031e7c
• /dev/sda
• /dev/systemdisk (using an udev rule)

OpenLMI does not assume any site policy, it’s up to system administrator to write udev rules if default /dev/sdX and /dev/disk/by-id/XYZ is not sufficient.

As many things in Linux are configurable and tunable, term SHOULD below means unless explicitly reconfigured.

CIM_StorageExtent

When OpenLMI builds CIM_StorageExtent for a block device, it fills following properties:

DeviceID

OpenLMI internal identifier of a block device. It should be opaque for applications, i.e. applications should not parse it / interpret it in any way.

• Guaranteed to be unique in the managed system.
• SHOULD be persistent across reboots.

Name

Canonical path to the device, such as as /dev/sda, /dev/mapper/test-test1, /dev/md/blivet00. This is the Linux default device name.

• Guaranteed to be unique in the managed system.
• Not persistent across reboots.

ElementName

Name of the block device, logical volume, RAID etc, such as as sda for disk, test1 for logical volume, blivet00 for MD RAID.

• Not unique in the managed system.
• Not persistent across reboots.
• Usually assigned by system administrator when the device is created (logical volume, MD RAID, ...)

Names

Array of all paths, under which this device is known in the system. All these paths are links to one block device. For disk from the example above, it’s content would be:

[
    '/dev/disk/by-id/ata-Samsung_SSD_840_Series_S19MNSAD500335K',
    '/dev/disk/by-id/wwn-0x50025385a0031e7c',
    '/dev/sda',
    '/dev/systemdisk;
]

Applications can use any of these properties to find an block device (using CQL or WQL).

LMI_VGStoragePool

Although volume groups are not exactly block devices, there are several ways how to identify LMI_VGStoragePool instances:

InstanceID

OpenLMI internal identifier of a volume group. It should be opaque for applications, i.e. applications should not parse it / interpret it in any way.

• Guaranteed to be unique in the managed system.
• SHOULD be persistent across reboots.

PoolID, ElementName

Name of the volume group.

• Guaranteed to be unique among all volume groups on the managed system. However, there can be other ManagedElements, such as logical volumes, with the same ElementName.
• SHOULD be persistent across reboots.