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PERC 6 controllers are designed to provide

enhanced performance, simplified man-

agement, increased reliability and fault

tolerance, optimized deployment with

Dell PowerVault storage, and flexible RAID

configuration and management tools."

allocations based on the characteristics of

the storage environment. This auto-tuning

feature helps administrators avoid the time-

consuming effort of manually tuning the

controller cache in a test environment.

Administrators can also perform real-

time RAID-level migration by converting

one RAID level to a different RAID level.

Figure 3 lists possible RAID-level migra-

tions and the number of drives required

at the beginning and end of the process.

RAID-level migration and expansion

cannot be performed on RAID-10,

RAID-50, or RAID-60 configurations.

IncreaSed relIabIlIty and

fault tolerance

Beyond industry-standard RAID levels,

PERC 6 controllers offer myriad features

to help protect data, including advanced

media error protection, enhanced rebuild

capabilities, consistency check and

background initialization, and other

key features such as Self-Monitoring,

Analysis, and Reporting Technology

(SMART), failed physical disk detection,

and hot spares.

advanced media error protection

PERC 6 controllers provide advanced

media error monitoring and repair tech-

nologies designed to prevent data loss

and enable safe data retrieval. For exam-

ple, a typical response to a media error in

a RAID controller would be to read the

data from the redundant disk and con-

tinue on. However, when a PERC 6

encounters media errors during normal

read and write operations, it can immedi-

ately attempt to repair the data. This

on-the-fly media error repair capability

helps increase data reliability by fixing data

written to bad media sectors, thus helping

reduce the potential for data loss.

Preemptive media error monitoring

through disk scanning services is typically

essential for enterprise-class RAID con-

trollers. While a typical approach to this

monitoring would employ a background

consistency check to scan for media

errors, the Patrol Read feature of PERC 6

controllers implements verify commands

to help validate media—a method that can

help significantly increase efficiency, par-

ticularly when encountering multiple

media errors on drives in an array.

enhanced rebuild capabilities

When an array is in degraded mode fol-

lowing a disk failure, the risk for potential

data loss increases—particularly if the

Source raId level

target raId level

RAID-0

RAID-1

RAID-0

RAID-5

RAID-0

RAID-6

RAID-1

RAID-0

RAID-1

RAID-5

RAID-1

RAID-6

RAID-5

RAID-0

RAID-5

RAID-6

RAID-0

RAID-6

RAID-5

Figure 3.

Possible RAID migrations supported with Dell PERC 6 controllers

controller encounters media errors on

optimal disks in the array during a rebuild.

In contrast to controllers that might imme-

diately stop the rebuild, the PERC 6 con-

tinues the rebuild to the end, allowing

administrators to access all valid data on

the virtual disk even though data has been

lost on the virtual disk stripe where the

media error occurred.

consistency check and background

initialization

The consistency check operation helps

verify the correctness of data in logical

drives that use RAID levels 1, 5, 6, 10, 50,

and 60 (RAID level 0 does not provide

data redundancy). For example, in a

system with parity, checking consistency

means computing the data on one drive

and comparing the results to the contents

of the parity drive. Dell recommends that

administrators perform a consistency

check at least once a month to help main-

tain optimum array status.

Background initialization is a consis-

tency check that is forced when creating

a logical drive, and automatically begins

five minutes after the drive has been

created. This operation checks for media

errors on physical disks and helps ensure

that striped data segments are the

same on all physical drives in an array.

required number of

source physical disks

target physical disks

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