Dell PowerVault MD3000 - Manual (Page 6)

6
Introduction
Introduction to Storage Arrays
A storage array includes various hardware components, such as physical disks,
RAID controller modules, fans, and power supplies, gathered into enclosures.
An enclosure containing physical disks accessed through RAID controller
modules is called a RAID enclosure.
One or more hosts attached to the array can access the data on the storage
array. You can also establish multiple physical paths between the host(s) and
the array so that the loss of any single path (through failure of a host port, for
example) does not result in loss of access to the data stored on the array.
The storage array is managed by MD Storage Manager software running
either on a host or on a storage management station. On a host system, MD
Storage Manager and the array communicate management requests and
event information directly via interface cables. On a storage management
station, MD Storage Manager communicates with the array either through an
ethernet connection on the RAID controller modules or via the host agent
installed on the host server.
With MD Storage Manager, you configure the physical disks in the array into
logical components called disk groups. You can then divide the disk groups
into virtual disks. You can make as many disk groups and virtual disks as your
storage array configuration and hardware permit. Disk groups are created in
the unconfigured capacity of a storage array and virtual disks are created in
the free capacity of a disk group.
Unconfigured capacity is comprised of the physical disks not already assigned
to a disk group. When a virtual disk is created using unconfigured capacity, a
disk group is automatically created. If the only virtual disk in a disk group is
deleted, then the disk group is also deleted. Free capacity is space in a disk
group that has not been assigned to a virtual disk.
Data is written to the physical disks in the storage array using RAID
technology. RAID levels define the way in which data is written to physical
disks. Different RAID levels offer different levels of accessibility, redundancy,
and capacity. You can set a specified RAID level for each disk group and
virtual disk on your storage array.
You can provide an additional layer of data redundancy by creating hot spares
in a disk group that has a RAID level other than 0. Hot spares can
automatically replace physical disks marked as Failed.