Users guide

19 Intel® RAID Software User Guide
2.3 RAID Configuration Strategies
The most important factors in RAID array configuration are:
• Virtual disk availability (fault tolerance)
• Virtual disk performance
• Virtual disk capacity
You cannot configure a virtual disk that optimizes a
ll three factors, but it is easy to choose
a virtual disk configuration that maximizes one factor at the expense of another factor. For
example, RAID 1 (mirroring) provides excellent fault tolerance, but requires a redundant
drive. The following subsections describe how to use the RAID levels to maximize virtual
disk availability (fault tolerance), virtual disk performance, and virtual disk capacity.
2.3.1 Maximizing Fault Tolerance
Fault tolerance is achieved through the ability to perform automatic and transparent
rebuilds using hot-spare drives and hot swaps. A hot-spare drive is an unused online
available drive that the RAID controller instantly plugs into the system when an active
drive fails. After the hot spare is automatically moved into the RAID array, the failed
drive is automatically rebuilt on the spare drive. The RAID array continues to handle
requests while the rebuild occurs.
A hot swap is the manual substitution of a replacement unit in a disk subsystem for a
defective one, where the substitution can be performed while the subsystem is running
hot-swap drives. Auto-Rebuild in the WebBIOS Configuration Utility allows a failed
drive to be replaced and automatically rebuilt by “hot swapping” the drive in the same
drive bay. The RAID array continues to handle requests while the rebuild occurs,
providing a high degree of fault tolerance and zero downtime.
Table 9. RAID Levels and Fault Tolerance
RAID
Level
Fault Tolerance
0 Does not provide fault tolerance. All data is
lost if any drive fails. Disk striping writes
data across multiple disk drives instead of just one disk drive. It involves partitioning
each drive storage space into stripes that can vary in size. RAID 0 is ideal for
applications that require high bandwidth but do not require fault tolerance.
1 or
IME
Provides complete data redundancy. If one drive fa
ils, the contents of the other drive
can be used to run the system and reconstruct the failed drive. The primary advantage
of disk mirroring is that it provides 100 percent data redundancy. Since the contents of
the drive are completely written to a second drive, no data is lost if one of the drives
fails. Both drives contain the same data at all times. RAID 1 or IME is ideal for any
application that requires fault tolerance and minimal capacity.