Dell PowerVault MD3820f - Manual (Page 23)

State Description
function properly, but performance may be affected
and additional disk failures may result in data loss.
Offline A virtual disk with one or more member disks in an
inaccessible (failed, missing, or offline) state. Data on
the virtual disk is no longer accessible.
Force online The storage array forces a virtual disk that is in an
Offline state to an Optimal state. If all the member
physical disks are not available, the storage array
forces the virtual disk to a Degraded state. The
storage array can force a virtual disk to an Online
state only when a sufficient number of physical disks
are available to support the virtual disk.
Disk Pools
Disk pooling allows you to distribute data from each virtual disk randomly across a set of physical disks.
Although there is no limit on the maximum number of physical disks that can comprise a disk pool, each
disk pool must have a minimum of 11 physical disks. Additionally, the disk pool cannot contain more
physical disks than the maximum limit for each storage array.
Thin Virtual Disks
Thin virtual disks can be created from an existing disk pool. Creating thin virtual disks allows you to set up
a large virtual space, but only use the actual physical space as you need it.
RAID Levels
RAID levels determine the way in which data is written to physical disks. Different RAID levels provide
different levels of accessibility, redundancy, and capacity.
Using multiple physical disks has the following advantages over using a single physical disk:
• Placing data on multiple physical disks (striping) allows input/output (I/O) operations to occur
simultaneously and improve performance.
• Storing redundant data on multiple physical disks using mirroring or parity supports reconstruction of
lost data if an error occurs, even if that error is the failure of a physical disk.
Each RAID level provides different performance and protection. You must select a RAID level based on
the type of application, access, fault tolerance, and data you are storing.
The storage array supports RAID levels 0, 1, 5, 6, and 10. The maximum and minimum number of physical
disks that can be used in a disk group depends on the RAID level:
• 120 (180 with PFK) for RAID 0, 1, and 10
• 30 for RAID 5 and 6
Maximum Physical Disk Support Limitations
Although PowerVault MD Series storage arrays with premium feature kit can support up to 180 physical
disks, RAID 0 and RAID 10 configurations with more than 120 physical disks are not supported. MD
23