Implementing the IBM Storwize V5000

14 Implementing the IBM Storwize V5000

1.5.6 Managed disks

An MDisk refers to the unit of storage that IBM Storwize V5000 virtualizes. This unit can be a

logical volume on an external storage array that is presented to the IBM Storwize V5000 or a

RAID array that consists of internal drives. The IBM Storwize V5000 then can allocate these

MDisks into storage pools.

An MDisk is invisible to a host system on the storage area network because it is internal to the

IBM Storwize V5000 system.

An MDisk features the following modes:

򐂰 Array

Array mode MDisks are constructed from internal drives by using the RAID functionality.

Array MDisks are always associated with storage pools.

򐂰 Unmanaged

LUNs presented by external storage systems to IBM Storwize V5000 are discovered as

unmanaged MDisks. The MDisk is not a member of any storage pools, which means it is

not being used by the IBM Storwize V5000 storage system.

򐂰 Managed

Managed MDisks are LUNs presented by external storage systems to an IBM Storwize

V5000 that are assigned to a storage pool and provide extents so that volumes can use it.

Any data that might be on these LUNs when they are added is lost.

򐂰 Image

Image MDisks are LUNs that are presented by external storage systems to an IBM

Storwize V5000 and assigned directly to a volume with a one-to-one mapping of extents

between the MDisk and the volume. For more information, see Chapter 6, “Storage

migration wizard” on page 237.

1.5.7 Quorum disks

A quorum disk is an MDisk that contains a reserved area for use exclusively by the system. In

the IBM Storwize V5000, internal drives can be considered as quorum candidates. The

clustered system uses quorum disks to break a tie when exactly half the nodes in the system

remain after a SAN failure.

The clustered system automatically forms the quorum disk by taking a small amount of space

from an MDisk. It allocates space from up to three different MDisks for redundancy, although

only one quorum disk is active.

To avoid the possibility of losing all of the quorum disks because of a failure of a single

storage system if the environment has multiple storage systems, you should allocate the

quorum disk on different storage systems. It is possible to manage the quorum disks by using

the CLI.

1.5.8 Storage pools

A storage pool is a collection of MDisks (up to 128) that are grouped to provide capacity for

volumes. All MDisks in the pool are split into extents of the same size. Volumes are then

allocated out of the storage pool and are mapped to a host system.