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Creating logical units

You can create logical units and assign the logical units to virtual server adapters by using the Virtual I/O Server (VIOS) command-line interface.

A logical unit provides the backing storage for the virtual volume of a client partition. By using the following procedure, you can assign a logical unit for each client partition from the shared storage pool of a cluster. Subsequently, you can map the logical unit to the virtual server adapter associated with the virtual Small Computer Serial Interface (SCSI) adapter of the client partition by using the Hardware Management Console (HMC).

When the mapping operations are complete, the logical unit path is similar to the following example:

SAN Storage <=> poolA <=> luA1 <=> viosA1 vtscsi0 <=> viosA1 vhost0 <=> client1 vscsi0 <=> client hdisk0.

Notes:

A single logical unit can be mapped by multiple virtual server adapters, and thus, accessed by multiple client partitions. However, this mapping typically requires either an additional software layer such as a database management system or the use of the Persistent Reserves standard to manage access to the shared logical unit.
A logical unit can be mapped from multiple VIOS partitions to a single virtual client.

To create logical units and assign the logical units to virtual server adapters, complete the following steps:

Obtain the physical location identifiers for the virtual server adapters by running the lsmap command. For example, entering the lsmap -all command returns results similar to the following:
```
SVSA            Physloc                              Client Partition ID
--------------------------------------------------------------------------
vhost0          U8203.E4A.10D4451-V4-C12             0x00000000

VTD             NO VIRTUAL TARGET DEVICE FOUND
SVSA            Physloc                              Client Partition ID
--------------------------------------------------------------------------
vhost1          U8203.E4A.10D4451-V4-C13             0x00000000
```
Where, Physloc identifies the VIOS virtual server adapter related to the HMC property for the viosA1 VIOS logical partition illustrated in the following figure.
Where:
- -C12 of the vhost0 virtual SCSI adapter physloc corresponds to the server SCSI adapter ID 12, which maps to virtual SCSI adapter 4 on the client1 client partition with ID 2
- -C13 of the vhost1 virtual SCSI adapter physloc corresponds to the server SCSI adapter ID 13, which maps to virtual SCSI adapter 3 on the client2 client partition with ID 7
The virtual target devices (VTD) also consist of a Physloc field. However, the Physloc field is empty for VTDs because the HMC property is not applicable to a VTD.
Create the logical unit by running the mkbdsp command. For example:
- The luA1 logical unit is created in the poolA storage pool of the clusterA cluster, with thin-provisioning and an initial provisional size of 100 MB.
```
mkbdsp -clustername clusterA -sp poolA 100M -bd luA1
```
- The luA3 logical unit is created in the poolA storage pool of the clusterA cluster, with thick-provisioning and an initial provisional size of 100 MB.
```
mkbdsp -clustername clusterA -sp poolA 100M -bd luA3 -thick
```
Map the logical unit to the virtual server adapter associated with the client partition by running the mkbdsp command. For example:
- The luA1 logical unit is thin-provisioned and mapped to the vscsi0 virtual server adapter associated with the client1 client partition, which the HMC properties and the lsmap command indicate as vhost0.
```
mkbdsp -clustername clusterA -sp poolA -bd luA1 -vadapter vhost0
```
- The luA3 logical unit is thick-provisioned and mapped to the vscsi0 virtual server adapter associated with the client1 client partition, which the HMC properties and the lsmap command indicate as vhost0.
```
mkbdsp -clustername clusterA -sp poolA -bd luA3 -vadapter vhost0 -thick
```
Create the logical unit in the shared storage pool, and map it to the virtual server adapter associated with the client partition. For example:
- The luA2 logical unit is created in the poolA storage pool of the clusterA cluster, with thin-provisioning and an initial provisional size of 200 MB. The luA2 logical unit is then mapped to the vscsi0 virtual server adapter associated with the client2 client partition, which the HMC properties and the lsmap command indicate as vhost1.
```
mkbdsp -clustername clusterA -sp poolA 200M -bd luA2 -vadapter vhost1 -tn vtscsi1
```
- The luA4 logical unit is created in the poolA storage pool of the clusterA cluster, with thick-provisioning and an initial provisional size of 200 MB. The luA4 logical unit is then mapped to the vscsi0 virtual server adapter associated with the client2 client partition, which the HMC properties and the lsmap command indicate as vhost1.
```
mkbdsp -clustername clusterA -sp poolA 200M -bd luA4 -vadapter vhost1 -tn vtscsi1 -thick
```
Note: The -tn vtscsiX option is not mandatory. If this option is omitted, a default value is used. By specifying the virtual target name, you can run the lsdevinfo command and search for information using the target name. In addition, you can map multiple logical units to the same virtual host adapter. The virtual target name is used to distinguish the mappings.

Display the logical unit information. For example, entering the lssp -clustername clusterA -sp poolA -bd command returns results similar to the following. Here, the logical unit is the backing device, or bd.

LU Name   Size (MB)    ProvisionType   %Used Unused(mb) LU UDID
-----------------------------------------------------------------------------------------
luA1      100          THIN            10%   90         258f9b298bc302d9c7ee368ff50d04e3
luA2      200          THIN            15%   170        7957267e7f0ae3fc8b9768edf061d2f8
luA3      100          THICK           5%    95         459f9b298bc302fc9c7ee368f50d04e3
luA4      200          THICK           0%    200        6657267e7d0ae3fc7b9768edf061d2d2

Entering the lsmap -all command returns results similar to the following:

SVSA            Physloc                                      Client Partition ID
--------------------------------------------------------------------------------------
vhost0          U8203.E4A.10D4451-V4-C12                     0x00000002

VTD                   vtscsi0
Status                Available
LUN                   0x8100000000000000
Backing device        lua1.b1277fffdd5f38acb365413b55e51638
Physloc                
Mirrored              N/A

VTD                   vtscsi1
Status                Available
LUN                   0x8200000000000000
Backing device        lua2.8f5a2c27dce01bf443383a01c7f723d0
Physloc                
Mirrored              N/A

In the examples in this topic, the vscsi0 virtual client SCSI adapter on client partitions Client1 and Client2 was mapped to the logical units luA1 and luA2.

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Last updated: Thu, April 05, 2018