Logical Volume Management¶

Volume Groups (VG) are represented by, LMI_VGStoragePool class.

Every LMI_VGStoragePool instance has associated one instance of LMI_VGStorageSetting representing its configuration (e.g. volume group extent size) and one instance of LMI_LVStorageCapabilities, representing its ability to create logical volumes (for SMI-S applications).

Physical Volumes (PV) are associated to VGs using LMI_VGAssociatedComponentExtent association.

Logical Volumes (LV) are represented by LMI_LVStorageExtent class. Each LMI_LVStorageExtent instance is associated to its VG using LMI_LVAllocatedFromStoragePool association.

In addition, LVs are associated to all PVs using LMI_LVBasedOn association.

Following instance diagram shows one Volume Group /dev/myGroup based on three Physical Volumes /dev/sda1, /dev/sdb1 `` and ``/dev/sdc1 and two Logical Volumes myVol1 and myVol2.

Note that the diagram is simplified and does not show LMI_LVBasedOn association, which associates every myVolY to /dev/sdX1.

Currently the LVM support is limited to creation and removal of VGs and LVs. It is not possible to modify existing VG or LV, e.g. add or remove devices to/from VG and/or resize LVs. In future OpenLMI may be extended to have more configuration options in LMI_VGStorageSetting and LMI_LVStorageSetting.

Useful methods¶

CreateOrModifyVG: Creates a Volume Group with given devices. The devices are automatically formatted with Physical Volume metadata. Optionally, the Volume group extent size can be specified by using Goal parameter of the method.
CreateOrModifyStoragePool: Creates a Volume Group in SMI-S way.
CreateVGStorageSetting: This is helper method to calculate LMI_VGStorageSetting for given list of devices for CreateOrModifyStoragePool method.
CreateOrModifyLV: Creates a Logical Volume from given VG.
CreateOrModifyElementFromStoragePool: Creates a Logical Volume in SMI-S way.
DeleteLV: Destroys a Logical Volume.
ReturnToStoragePool: Destroys a Logical Volume in SMI-S way.
DeleteVG: Destroys a Volume Group.
DeleteStoragePool: Destroys a Volume Group in SMI-S way.

Use cases¶

Create Volume Group¶

Use CreateOrModifyVG method. Following example creates a VG ‘/dev/myGroup’ with three members and with default extent size (4MiB):

# Find the devices we want to add to VG
# (filtering one CIM_StorageExtent.instances()
# call would be faster, but this is easier to read)
sda1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sda1")
sdb1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sdb1")
sdc1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sdc1")

# Create the VG
(ret, outparams, err) = storage_service.CreateOrModifyVG(
        ElementName = "myGroup",
        InExtents= [sda1.path, sdb1.path, sdc1.path])
vg = outparams['pool'].to_instance()
print "VG", vg.PoolID, \
        "with extent size", vg.ExtentSize, \
        "and",  vg.RemainingExtents, "free extents created."

The resulting VG is the same as shown in diagram above, except it does not have any LVs yet.

Create Volume Group in SMI-S way¶

SMI-S applications can use CreateOrModifyStoragePool method. Following example creates a VG ‘/dev/myGroup’ with three members and with default extent size (4MiB):

# Find the devices we want to add to VG
# (filtering one CIM_StorageExtent.instances()
# call would be faster, but this is easier to read)
sda1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sda1")
sdb1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sdb1")
sdc1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sdc1")

# Create the VG
(ret, outparams, err) = storage_service.CreateOrModifyStoragePool(
        InExtents=[sda1.path, sdb1.path, sdc1.path],
        ElementName="myGroup")
vg = outparams['pool'].to_instance()
print "VG", vg.PoolID, \
        "with extent size", vg.ExtentSize, \
        "and",  vg.RemainingExtents, "free extents created."

The resulting VG is the same as shown in diagram above, except it does not have any LVs yet.

Create Volume Group with specific extent size¶

Use CreateVGStorageSetting to create LMI_VGStorageSetting, modify its ExtentSize property with desired extent size and finally call CreateOrModifyVG with the setting as Goal parameter. Following example creates a VG ‘/dev/myGroup’ with three members and with 1MiB extent size (4MiB):

# Find the devices we want to add to VG
# (filtering one CIM_StorageExtent.instances()
# call would be faster, but this is easier to read)
sda1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sda1")
sdb1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sdb1")
sdc1 = root.CIM_StorageExtent.first_instance(
        Key="DeviceID", Value="/dev/sdc1")

# Create the LMI_VGStorageSetting
vg_caps = root.LMI_VGStorageCapabilities.first_instance()
(ret, outparams, err) = vg_caps.CreateVGStorageSetting(
        InExtents = [sda1.path, sdb1.path, sdc1.path])
setting = outparams['setting'].to_instance()
setting.ExtentSize = MEGABYTE
# TODO: modify the instance

# Create the VG
# (either of CreateOrModifyStoragePool or CreateOrModifyVG
# can be used with the same result)
(ret, outparams, err) = storage_service.CreateOrModifyStoragePool(
        InExtents=[sda1.path, sdb1.path, sdc1.path],
        ElementName="myGroup",
        Goal = setting.path)
vg = outparams['pool'].to_instance()
print "VG", vg.PoolID, \
        "with extent size", vg.ExtentSize, \
        "and",  vg.RemainingExtents, "free extents created."

List Physical Volumes of a Volume Group¶

Enumerate VGAssociatedComponentExtent associations of the VG.

Following code lists all PVs of /dev/myGroup:

# Find the disk
vg = root.LMI_VGStoragePool.first_instance(
        Key="InstanceID", Value="LMI:VG:myGroup")
pvs = vg.associators(AssocClass="LMI_VGAssociatedComponentExtent")
for pv in pvs:
    print "Found PV", pv.DeviceID

Create Logical Volume¶

Use CreateOrModifyLV method. Following example creates two 100MiB volumes:

# Find the VG
vg = root.LMI_VGStoragePool.first_instance(
        Key="InstanceID", Value="LMI:VG:myGroup")

# Create the LV
(ret, outparams, err) = storage_service.CreateOrModifyLV(
        ElementName = "Vol1",
        InPool = vg.path,
        Size = 100 * MEGABYTE)
lv = outparams['theelement'].to_instance()
print "LV", lv.DeviceID, \
        "with", lv.BlockSize * lv.NumberOfBlocks,\
        "bytes created."

# Create the second LV
(ret, outparams, err) = storage_service.CreateOrModifyLV(
        ElementName = "Vol2",
        InPool = vg.path,
        Size = 100 * MEGABYTE)
lv = outparams['theelement'].to_instance()
print "LV", lv.DeviceID, \
        "with", lv.BlockSize * lv.NumberOfBlocks, \
        "bytes created."

The resulting LVs are the same as shown in diagram above.

Create Logical Volume in SMI-S way¶

Use CreateOrModifyElementFromStoragePool method. The code is the same as in previous sample, just different method is used:

# Find the VG
vg = root.LMI_VGStoragePool.first_instance(
        Key="InstanceID", Value="LMI:VG:myGroup")

# Create the LV
(ret, outparams, err) = storage_service.CreateOrModifyLV(
        ElementName = "Vol1",
        InPool = vg.path,
        Size = 100 * MEGABYTE)
lv = outparams['theelement'].to_instance()
print "LV", lv.DeviceID, \
        "with", lv.BlockSize * lv.NumberOfBlocks,\
        "bytes created."

# Create the second LV
(ret, outparams, err) = storage_service.CreateOrModifyElementFromStoragePool(
        ElementName = "Vol2",
        InPool = vg.path,
        Size = 100 * MEGABYTE)
lv = outparams['theelement'].to_instance()
print "LV", lv.DeviceID, \
        "with", lv.BlockSize * lv.NumberOfBlocks, \
        "bytes created."

Delete VG¶

Call DeleteVG method:

vg = root.LMI_VGStoragePool.first_instance(
        Key="InstanceID", Value="LMI:VG:myGroup")
(ret, outparams, err) = storage_service.DeleteVG(
        Pool = vg.path)

Delete LV¶

Call DeleteLV method:

lv = root.LMI_LVStorageExtent.first_instance(
        Key="ElementName", Value="Vol2")
(ret, outparams, err) = storage_service.DeleteLV(
        TheElement = lv.path)

Future direction¶

In future, we might implement:

Modification of existing VGs and LVs, for example adding/removing devices and resizing LVs.
LVs with stripping and mirroring.
Clustered VGs and LVs.
Indications of various events, like RAID failed member, synchronization errors etc.

Logical Volume Management¶

Useful methods¶

Use cases¶

Create Volume Group¶

Create Volume Group in SMI-S way¶

Create Volume Group with specific extent size¶

List Physical Volumes of a Volume Group¶

Create Logical Volume¶

Create Logical Volume in SMI-S way¶

Delete VG¶

Delete LV¶

Future direction¶

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Logical Volume Management¶

Useful methods¶

Use cases¶

Create Volume Group¶

Create Volume Group in SMI-S way¶

Create Volume Group with specific extent size¶

List Physical Volumes of a Volume Group¶

Create Logical Volume¶

Create Logical Volume in SMI-S way¶

Delete VG¶

Delete LV¶

Future direction¶

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