Adding disks to an existing disk array

Some controllers support adding disks to existing RAID level 5 or 6 disk arrays, which allows you to dynamically increase the capacity of a disk array while preserving its existing data.

After you add disks to an existing disk array, they are protected and become part of the disk array but will not contain parity and the data will not be restriped. Use of this feature, however, will result in a performance penalty. The first part of the performance penalty exists because not all the drives in the array contain parity and therefore the drives with parity are accessed more often for parity updates. The second part of the performance penalty comes from the data not being restriped and therefore reducing the ability to use the hardware assisted stripe write features.

An Array Candidate pdisk is not necessarily a candidate that can be added to an existing array. In addition to being an Array Candidate, the pdisk must also be recognized by the adapter as having its data zeroed. This situation ensures that when the disks are added to the array, the parity data will be correct and the array will remain protected against disk failures.

To add disks to an existing array, do the following:

Note: Not all controllers support adding disks to an existing array. See the feature comparison tables for PCIe3, PCIe2, PCIe and PCI-X cards to look for controllers that contain this support.

Ensure that the disks to be added are Zeroed Array Candidate pdisks. For information about viewing and changing the state of the disk, see Preparing disks for use in SAS disk arrays and Viewing the disk array configuration.
Start the IBM® SAS Disk Array Manager by following the steps in Using the Disk Array Manager.
Select Add Disks to an Existing SAS Disk Array.

Select the IBM SAS Disk Array to which you want to add disks.

A screen will display similar to the following example. If a particular disk is not included in the list, it might not be a candidate that can be added to the array because of the following reasons:

The disk's capacity is less than that of the smallest disk already in the array.
The disk has not been formatted as a 528 bytes per sector Array Candidate pdisk.
The disk does not have its data zeroed.

For the second and third cases, the disk can be added to an array if it is first formatted using the Create an Array Candidate pdisk and Format to 528 Byte Sectors option in the IBM SAS Disk Array Manager.


+--------------------------------------------------------------------------------+

|                Add Disks to an Existing SAS Disk Array                         |

| Move cursor to desired item and press F7. Use arrow keys to scroll.            |

|     ONE OR MORE items can be selected.                                         |

| Press Enter AFTER making all selections.                                       |

|                                                                                |

|   # Choose up to 14 of the following disks to add to hdisk2                    |

|                                                                                |

|   pdisk16   00000600  Active      Array Candidate         69.7GB Zeroed        |

|   pdisk17   00000800  Active      Array Candidate         69.7GB Zeroed        |

|   pdisk18   00040800  Active      Array Candidate         69.7GB Zeroed        |

|                                                                                |

|   # Note: If a disk is not listed here it is either not a candidate            |

|   # to be added to this array or it does not have its data zeroed              |

|   # Use the Create an Array Candidate pdisk and Format to 528 Byte             |

|   # Sectors option to format and zero the disk.                                |

|                                                                                |

| F1=Help                 F2=Refresh              F3=Cancel                      |

| F7=Select               F8=Image                F10=Exit                       |

| Enter=Do                /=Find                  n=Find Next                    |

+--------------------------------------------------------------------------------+

Press Enter to add the disks to the array.

To enable higher level components in the system to use the increased capacity of the disk array, additional steps might be needed.

Last updated: Wed, May 24, 2017