60 IBM Flex System V7000 Storage Node Introduction and Implementation Guide
2.5.6 Managed disks
A managed disk (MDisk) refers to the unit of storage that IBM Flex System V7000 Storage
Node virtualizes. This unit could be a logical volume from an external storage array presented
to the IBM Flex System V7000 Storage Node or a RAID array created on internal drives, or an
external Storwize V7000 expansion that is managed by the IBM Flex System V7000 Storage
Node. The IBM Flex System V7000 Storage Node can allocate these MDisks into various
storage pools for different usage or configuration needs.
An MDisk should not be visible to a host system on the storage area network, as it should
only be zoned to the IBM Flex System V7000 Storage Node system.
An MDisk has four possible modes:
Array:
Array mode MDisks are constructed from drives using the RAID function. Array MDisks
are always associated with storage pools.
Unmanaged:
Unmanaged MDisks are not being used by the system. This situation might occur when an
MDisk is first imported into the system, for example.
Managed:
Managed MDisks are assigned to a storage pool and provide extents so that volumes can
use it.
Image:
Image MDisks are assigned directly to a volume with a one-to-one mapping of extents
between the MDisk and the volume. This situation is normally used when importing logical
volumes into the clustered system that already have data on them, which ensures that the
data is preserved as it is imported into the clustered system.
2.5.7 Quorum disks
A quorum disk is a managed disk (MDisk) that contains a reserved area for use exclusively by
the system. In the IBM Flex System V7000 Storage Node, any managed disks can be
considered as a quorum candidate. The clustered system uses quorum disks to break a tie
when exactly half the control canisters in the system remain active after a SAN failure. The
IBM Flex System V7000 Storage Node dynamically assigns which quorum drive will be the
active member (DQ).
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