Hardware Architecture (X vs. C): Pure Storage maintains two primary FlashArray lines: the FlashArray//X (performance-oriented) and the FlashArray//C (capacity-oriented).

Flash Types (TLC vs. QLC):

FlashArray//X (like the X20R4 mentioned in the question) uses TLC (Triple-Level Cell) DirectFlash Modules (DFMs). TLC provides high performance and high endurance, which is necessary for latency-sensitive mission-critical workloads.

FlashArray//C uses QLC (Quad-Level Cell) DirectFlash Modules. QLC provides significantly higher density at a lower cost per GB, but it has different performance and endurance profiles compared to TLC.

Compatibility Constraints: Purity//FA is designed to manage specific flash geometries. QLC modules are not compatible with the //X series arrays. The controller logic and software-defined flash management in an X20R4 are tuned for the voltage and timing characteristics of TLC flash.

The Admission Process: When a new data pack is inserted, the array performs a " handshake. " If the controller detects a module type that it is not hardware-qualified to support (in this case, QLC in an //X chassis), it will refuse to admit the capacity to prevent system instability or data integrity issues.

Why Option A is incorrect: Modern FlashArrays (since the //M series) use NVMe over a PCIe backplane for DirectFlash Modules. Pure moved away from SAS (Serial Attached SCSI) for its primary data drives years ago to eliminate the performance bottlenecks associated with the SAS protocol.

Why Option C is incorrect: An X20R4 uses TLC flash. If the data pack were TLC, it would likely be compatible (provided it met the minimum module count and Purity version requirements).