What is UNMAP?: UNMAP (SCSI command 0x42) is the mechanism that allows a host (like ESXi) to inform the storage array that specific blocks of data are no longer in use (e.g., after a VM is deleted or moved). This is critical for Pure Storage because it allows the array to reclaim that space and maintain high data reduction ratios.

Evolution in ESXi: In versions prior to 6.5, UNMAP was a manual process executed via the CLI. Starting with ESXi 6.7, VMware introduced Automatic Space Reclamation , which runs in the background.

The Pure Storage Recommendation: Pure Storage recommends setting the reclamation priority to Auto with Low Priority .

Low Priority: This ensures that the UNMAP commands are sent to the FlashArray at a steady, manageable rate (roughly up to 25 MB/s to 100 MB/s depending on the Purity version). Because FlashArrays are built on a high-performance metadata engine, " Low Priority " is more than sufficient to keep up with even high-churn environments without causing any contention for active application I/O.

Why avoid High Priority (Option B)?: Setting it to high priority or using a fixed high-burst rate can lead to " bursty " SCSI traffic. While the FlashArray can handle the load, it is considered a best practice to keep background maintenance tasks like space reclamation at a lower priority to ensure the " Big Three " (latency, bandwidth, IOPS) for production workloads remain optimized.

Verification: You can verify that UNMAP is working by looking at the Data Reduction metrics in the Purity GUI or Pure1. If the " Thin Provisioning " or " Reclaimed " numbers are increasing after file deletions, the host is correctly communicating its freed space to the array.