3PAR InForm® OS 2.2.4 Concepts Guide (320-200085 Rev B, March 2009)

2.3
3PAR Storage Concepts and Terminology
InForm OS Version 2.2.4 3PAR InForm OS Concepts Guide
■ One or more chunklets are allocated as spares. These spare chunklets are used to hold data
during disk failures and maintenance procedures that require data relocation. Any
chunklet can be reserved as a spare, but the system setup script selects those chunklets as
close to the end of the disk logical-block space as possible.
Appendix A, Sparing contains additional information about working with spare chunklets.
■ The remainder of the disk can be used for logical disks.
2.1.2 Logical Disks
A logical disk is a collection of physical disk chunklets that have been arranged as rows of RAID
sets. Each RAID set is made up of chunklets from different physical disks, where each chunklet
consists of 256 MB of contiguous space. A chunklet can be assigned to only one logical disk.
2.1.2.1 RAID Types
The 3PAR storage system supports three RAID types:
■ RAID 0
■ RAID 10 (RAID 1)
■ RAID 50 (RAID 5)
2.1.2.1.1 RAID 0
On a RAID 0 logical disk, data is striped across rows of chunklets on different physical disks. The
number of chunklets in a RAID 0 set is known as the set size, which is always 1 for a RAID 0
logical disk. The number of sets in a row is known as the row size. The system accesses data
from a RAID 0 logical disk in step sizes, where the step size is the number of contiguous bytes
that the system accesses before moving on to the next chunklet.
NOTE: The system may round up when creating logical disks to support virtual
volumes and Common Provisioning Groups (CPGs), resulting in a discrepancy
between the user-specified size or growth increment and the actual space
allocated to logical disks created by the system. For a detailed discussion of this
issue, see Logical Disk Size and RAID Type on page 7.3.