The FlashArray//X20R4-LL (Low-Line) model is a specific configuration designed for lower capacity and power entry points. Unlike the standard //X or //XL models which can support fully populated chassis and shelves, the "Low-Line" configurations often come with strict hardware limitations regarding power draw and drive count. A known constraint for specific Low-Line chassis upgrades, particularly when moving to the X20R4-LL, is a limitation on the number of DirectFlash Modules (drives) supported due to the power supply unit (PSU) capacity or thermal design targeted for that specific SKU.
In this scenario, if the source array (X20R3) was populated with more drives than the target X20R4-LL supports-specifically more than 10 drives-the upgrade validation checks (such as those performed by the upgrade script or Purity health checks) will flag a failure. Even though the voltage readings are technically correct (indicating the PDUs are providing power), the check fails because the hardware configuration exceeds the supported power budget for that specific chassis model.
Implementation Engineers must verify the drive count of the source array against the specifications of the target "Low-Line" array during the planning phase. If the source array has 11 or more drives, the target hardware cannot be an LL model; it would require a standard model to support the additional power load of the extra drives. This check prevents the array from booting into a state where it might experience power contention or thermal shutdown under load.
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