HP StorageWorks 1200r All-in-One Storage System - Manual (Page 52)

Fault tolerance
Drive failure, although rare, is potentially catastrophic. For example, using simple striping as shown
in
Figure 14 , failure of any hard drive leads to failure of all logical drives in the same array, and
hence to data loss.
To protect against data loss from hard drive failure, storage systems should be configured with fault
tolerance. HP recommends adhering to RAID 5 configurations.
The table below summarizes the important features of the different kinds of RAID supported by the
Smart Array controllers. The decision chart in the following table can help determine which option is
best for different situations.
Table 16 Summary of RAID methods
RAID 6 ADG
RAID 5
Distributed
Data Guarding
RAID 1+0
Mirroring
RAID 0
Striping (no
fault tolerance)
Storage system dependent 14 N/A N/A
Maximum number of hard
drives
Yes Yes Yes No
Tolerant of single hard
drive failure?
Yes (two drives can fail) No
If the failed
drives are not
mirrored to
each other
No
Tolerant of multiple
simultaneous hard drive
failures?
Online Spares
Further protection against data loss can be achieved by assigning an online spare (or hot spare) to
any configuration except RAID 0. This hard drive contains no data and is contained within the same
storage subsystem as the other drives in the array. When a hard drive in the array fails, the controller
can then automatically rebuild information that was originally on the failed drive onto the online spare.
This quickly restores the system to full RAID level fault tolerance protection. If using RAID Advanced
Data Guarding (ADG) the system is able to have two drive failures simultaneously; however, if the
third drive fails during this procedure, data will be lost.
Logical storage elements
Logical storage elements consist of those components that translate the physical storage elements to
file system elements. The storage system uses the Windows Disk Management utility to manage the
disks presented to the file system. The HP All-in-One Storage System supports the basic disk type of
LUN presentation; it does not support dynamic disks.
Logical drives (LUNs)
While an array is a physical grouping of hard drives, a logical drive consists of components that
translate physical storage elements into file system elements.
It is important to note that a LUN may extend over (span) all physical drives within a storage controller
subsystem, but cannot span multiple storage controller subsystems.
Storage management overview 52