AHCI and RAID on HP Compaq Elite 8000, 8100, 8200, and 8300 Business PCs - Technical White Paper

Hardware

The HP Elite 8000-series Business PCs uses Intel chipsets that support an AHCI capable Host Bus Adapter (HBA). This HBA

supports ATA and ATAPI devices in both PIO and DMA modes with NCQ as long as the device supports NCQ.

All hard drives shipped with the HP Elite 8000-series Business PCs are NCQ capable.

Limitations

NCQ functionality requires both HBA and hard drive to support it. Non-NCQ capable hard drives will not see any

performance benefits even though the HBA is NCQ capable.

Hot-plugging is not possible in an operating system without an AHCI driver that supports hot-plugging, such as DOS,

Windows 9x, Windows NT4.0, and older versions of Linux.

Changing AHCI to IDE Mode through the HP Replicated Setup Utility

Multiple AHCI systems can be reverted back to IDE mode using the HP Replicated Setup Utility. This utility allows for

system BIOS settings to be replicated and distributed throughout an enterprise. The procedures and information about

how to obtain the Replicated Setup Utility are described in the HP white paper “UEFI BIOS Tools for HP Business

Desktops” available at

http://h10032.www1.hp.com/ctg/Manual/c02932801.pdf .

Basic RAID Types

This section provides a brief explanation of the supported RAID configurations for HP Elite 8000-series Business PCs.

RAID 0 with two hard drives (Striped)

Even though HP supports RAID 0, it is not the recommended configuration for business PC users. Lack of redundancy

causes less than half the reliability of a single hard drive system since the Mean Time Between Failure (MTBF) of RAID 0

is equal to the MTBF of an individual drive, divided by the number of drives.

Table 3: RAID 0 with two hard drives (Striped)

First disk Second disk

Data Segment 1 Data Segment 2

Data Segment 3 Data Segment 4

Data Segment 5 Data Segment 6

Data Segment 7 Data Segment 8

Data Segment 9 Data Segment 10

Data Segment 11 Data Segment 12

Data Segment 13 Data Segment 14

Data Segment 15 Data Segment 16

In the previous table, each “Data Segment n” represents a group of data, known as a strip. In this case, each row

represents a stripe. RAID 0 represented in the table above shows how information is segmented, made into chunks or

strips, and stored across the stripes of the hard drive members of this RAID volume.

To better illustrate the concept of RAID 0 and striping, Figure 1 shows how a sequence of data “ABCD...” is stored in a

RAID 0 mode. In this example, each letter represents a segment or strip. The graphic shows how the various pieces of the

information go to different hard drives. If any segment of RAID 0 fails, all information from all members is lost.