Add pfSense NVMe cache overlay documentation

docs/ConfigExamples/Caching/pfSensenvmecacheuse.md

@@ -0,0 +1,76 @@
+---
+categories: [ConfigExample]
+FaqSection: operation
+---
+## Dscription
+This script creates a filesystem overlay using nullfs to mount an alternate NVMe-backed directory as the Squid cache location. On pfSense systems, the standard cache path (/var/squid/cache) is transparently redirected to a user-defined path on a different drive.
+The overlay itself functions correctly: Squid writes to and utilizes the new cache location as intended. However, the Clear Cache button in the pfSense GUI does not currently work with this setup. While this was the original goal of the project, this implementation is an important first step—it enables cache relocation without modifying Squid’s configured path, even though cache clearing still requires manual intervention.
+—
+J. Lee
+## Usage
+This script is intended for Netgate pfSense systems where Squid’s cache is normally located at:
+		/var/squid/cache
+When an alternate drive or filesystem (such as NVMe storage) is used for caching, management becomes more complex. In particular, the pfSense Clear Cache function does not operate correctly, requiring manual deletion of cache files.
+This script was created to simplify cache relocation by overlaying the default Squid cache path with a different storage location, while maintaining compatibility with pfSense’s expected directory structure.
+
+## add cron file
+		@reboot /root/mount_squid_nullfs.sh
+
+## Script .sh file used for cron job
+
+		#!/bin/sh
+
+		TAG="squid-nullfs"
+		NVME_DEV="/dev/nda0p2"
+		NVME_MNT="/nvme/LOGS_Optane"
+		CACHE_SRC="${NVME_MNT}/Squid_Cache"
+		CACHE_DST="/var/squid/cache"
+
+		# --- Helper function to log safely to system.log using pfSense PHP ---
+		log_sys() {
+		    MESSAGE="$1"
+		    logger -t "$TAG" "$MESSAGE"
+		}
+
+		log_sys "Starting Squid nullfs mount sequence"
+
+		# 1. Ensure NVMe filesystem is mounted
+		if ! mount | grep -q "on ${NVME_MNT} "; then
+		    log_sys "Mounting NVMe filesystem"
+		    mount_msdosfs "${NVME_DEV}" "${NVME_MNT}" || {
+		        log_sys "ERROR: NVMe mount failed"
+		        exit 1
+		    }
+		else
+		    log_sys "NVMe already mounted"
+		fi
+
+		# 2. Stop squid if running
+		if pgrep -x squid >/dev/null; then
+		    log_sys "Stopping squid"
+		    /usr/local/sbin/pfSsh.php playback svc stop squid
+		    sleep 2
+		fi
+
+		# 3. Ensure directories exist
+		mkdir -p "${CACHE_SRC}" "${CACHE_DST}"
+
+		# 4. Mount nullfs if not already mounted
+		if ! mount | grep -q "on ${CACHE_DST} "; then
+		    log_sys "Mounting nullfs cache"
+		    mount -t nullfs "${CACHE_SRC}" "${CACHE_DST}" || {
+		        log_sys "ERROR: nullfs mount failed"
+		        exit 1
+		    }
+		else
+		    log_sys "nullfs already mounted"
+		fi
+
+		# 5. Start squid
+		log_sys "Starting squid"
+		/usr/local/sbin/pfSsh.php playback svc start squid
+
+		log_sys "Squid nullfs mount completed"
+
+## Testing should show a valid mount on reboot in logs 
+<img width="690" height="226" alt="Screenshot 2026-01-12 at 14 56 06" src="https://github.com/user-attachments/assets/f770a6e0-b799-47dc-89fc-d5a05e25aef5" />