Adding MDisks to MDisk groups using the CLI

You can use the command-line interface (CLI) to add managed disks (MDisks) to MDisk groups.

The MDisks must be in unmanaged mode. Disks that already belong to an MDisk group cannot be added to another MDisk group until they have been deleted from their current MDisk group. You can delete an MDisk from an MDisk group under the following circumstances:

If the MDisk does not contain any extents in use by a virtual disk (VDisk)
If you can first migrate the extents in use onto other free extents within the group

Important: Do not add an MDisk using this procedure if you are mapping the MDisk to an image mode VDisk. Adding an MDisk to an MDisk group allows the SAN Volume Controller to write new data to the MDisk; therefore, any existing data on the MDisk is lost. If you want to create an image mode VDisk, use the svctask mkvdisk command instead of svctask addmdisk.

If you are using a SAN Volume Controller solid-state drive (SSD) managed disk, ensure that you are familiar with the SSD configuration rules.

When you are adding MDisks to an MDisk group using the svctask addmdisk command or when you are creating an MDisk group using the svctask mkmdiskgrp -mdisk command, the SAN Volume Controller performs tests on the MDisks in the list before the MDisks are allowed to become part of an MDisk group. These tests include checks of the MDisk identity, capacity, status and the ability to perform both read and write operations. If these tests fail or exceed the time allowed, the MDisks are not added to the group. However, with the svctask mkmdiskgrp -mdisk command, the MDisk group is still created even if the tests fail, but it does not contain any MDisks. If tests fail, confirm that the MDisks are in the correct state and that they have been correctly discovered.

The following events contribute to an MDisk test failure:

The MDisk is not visible to all SAN Volume Controller nodes in the cluster.
The MDisk identity has changed from a previous discovery operation.
The MDisk cannot perform read or write operations.
The status of the MDisk can be either degraded paths, degraded ports, excluded, or offline.
The MDisk does not exist.

The following events contribute to an MDisk test timeout:

The disk controller system on which the MDisk resides is failing.
A SAN fabric or cable fault condition exists that is preventing reliable communication with the MDisk.

Note: The first time that you add a new solid-state drive (SSD) to an MDisk group, the SSD is automatically formatted and set to a block size of 512 bytes.

Perform the following steps to add MDisks to MDisk groups:

Issue the svcinfo lsmdiskgrp CLI command to list the existing MDisk groups.

The following is an example of the CLI command you can issue to list the existing MDisk groups:

svcinfo lsmdiskgrp -delim :

The following is an example of the output that is displayed:

id:name:status:mdisk_count:vdisk_count:
capacity:extent_size:free_capacity:virtual_capacity:
used_capacity:real_capacity:overallocation:warning
0:mdiskgrp0:online:3:4:33.3GB:16:32.8GB:64.00MB:64.00MB:64.00MB:0:0
1:mdiskgrp1:online:2:1:26.5GB:16:26.2GB:16.00MB:16.00MB:16.00MB:0:0
2:mdiskgrp2:online:2:0:33.4GB:16:33.4GB:0.00MB:0.00MB:0.00MB:0:0

Issue the svctask addmdisk CLI command to add MDisks to the MDisk group.
The following is an example of the CLI command you can issue to add MDisks to an MDisk group:
```
svctask addmdisk -mdisk mdisk4:mdisk5:mdisk6:mdisk7 bkpmdiskgroup
```
Where mdisk4:mdisk5:mdisk6:mdisk7 are the names of the MDisks that you want to add to the MDisk group and bkpmdiskgroup is the name of the MDisk group for which you want to add the MDisks.