Administrator Guide

Table 2. Raid controller virtual disk states (continued)
State Description
storage array forces the virtual disk to a Degraded state. The storage
array can force a virtual disk to an Online state only when enough 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,
consistency, 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 replication or consistency 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 Storage Manager does not enforce 120-physical disk limit when
you setup a RAID 0 or RAID 10 configuration. Exceeding the 120-physical disk limit may cause your storage array to be unstable.
RAID level usage
To ensure best performance, you must select an optimal RAID level when you create a system physical disk. The optimal RAID level for
your disk array depends on:
• Number of physical disks in the disk array
• Capacity of the physical disks in the disk array
• Need for redundant access to the data (fault tolerance)
• Disk performance requirements
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