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Difficulty: HardStorage Devices and Interfaces

A server technician is upgrading a system by connecting SATA-based solid-state drives (SSDs) to an existing SAS backplane managed by a PCIe hardware RAID controller. The installation is successful. However, when the technician attempts the reverse configuration by connecting a SAS hard drive directly to a motherboard's native SATA controller port in a desktop system, the drive is not recognized and fails to function. Which of the following explains the technical reason for this outcome?

  1. SAS controllers and backplanes are engineered with backward compatibility for the SATA protocol, whereas native SATA controllers lack the software command set and signal logic required to communicate with SAS drives.Answer
  2. B
    The SAS drive requires an AHCI controller driver update within the desktop operating system before the native SATA motherboard port can negotiate protocol speed.
  3. C
    SAS drives require dedicated PCIe bus lanes for data transmission, which prevents standard motherboard SATA controllers from initializing them.
  4. D
    SATA motherboard ports supply insufficient electrical voltage to power the dual-port signaling logic built into enterprise SAS drives.

Answer

SAS host controllers and backplanes are designed with backward compatibility to accept SATA protocol drives through SATA Tunneling Protocol (STP), but native SATA motherboard controllers do not support SAS command sets or signaling logic, preventing SAS drives from working on SATA ports.
SAS hardware controllers and backplanes implement the SATA Tunneling Protocol (STP) to achieve backward compatibility with SATA hard drives and SSDs. However, this compatibility is strictly one-directional; native consumer SATA host controllers lack the physical hardware logic, dual-port signaling, and SCSI command set needed to communicate with SAS drives.

Step-by-Step Solution

1
Analyze SAS host controller capability with SATA drives.
SAS controllers include the SATA Tunneling Protocol (STP), allowing SATA drives to communicate smoothly when plugged into SAS backplanes.
Enterprise SAS standards were deliberately designed to be backward-compatible with lower-cost SATA drives.
2
Analyze native SATA controller capability with SAS drives.
SATA controllers only understand the SATA signaling protocol and AHCI/IDE command sets; they possess no understanding of SCSI command sets or SAS dual-port signaling.
Desktop SATA hardware is consumer-oriented and lacks the complex protocol translation hardware required for enterprise SAS drives.
3
Evaluate the outcome of connecting a SAS drive to a SATA controller.
The motherboard's SATA controller cannot initialize or communicate with the SAS drive, rendering it unrecognized.
Compatibility is strictly one-way (SAS controllers accept SATA drives, but SATA controllers do not accept SAS drives).

Key Concept

SAS and SATA Controller Backward Compatibility
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Topics

Storage Devices and Interfaces

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