Dell PERC 4/SI - Manual (Page 19)

Table 2 -9 provides an overview of RAID 50.
Table 2-9. RAID 50 Overview
Figure 2 -6 provides an example of a RAID 50 level logical drive.
Figure 2-6. RAID 50 Level Logical Drive
RAID Configuration Strategies
The most important factors in RAID array configuration are:
l Logical drive availability (fault tolerance)
l Logical drive performance
l Logical drive capacity
You cannot configure a logical drive that optimizes all three factors, but it is easy to choose a logical drive 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 logical drive availability (fault tolerance), logical drive performance, and logical drive capacity.
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 PERC 4/Di/Si and 4e/Di/Si instantly plug 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 BIOS 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 2 -10 describes the fault tolerance features of each RAID level.
Table 2-10. RAID Levels and Fault Tolerance
Uses Appropriate when used with data that requires high reliability, high request rates, high data transfer, and medium to large capacity.
Strong Points Provides high data throughput, data redundancy and very good performance.
Weak Points Requires 2 to 8 times as many parity drives as RAID 5.
Drives 6 to 28
Dell supports the use of two channels with a maximum of 14 physical drives per channel.
RAID
Level
Fault Tolerance
0 Does not provide fault tolerance. All data 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 performance but do
not require fault tolerance.
1 Provides complete data redundancy. If one disk drive fails, the contents of the other disk drive can be used to run the system and reconstruct the
failed drive. The primary advantage of disk mirroring is that it provides 100% data redundancy. Since the contents of the disk 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 is ideal for any application