On the status page (
https://m0n0wall-ip-address/status.php) In the "last 200 system log entries" section, I see this:
Nov 19 12:44:25 m0n0wall kernel: ad0: 15MB <PQI IDE DiskOnModule db01.17a> at ata0-master BIOSPIO
That is a 16MB Disk on Module IDE interface flash drive.
You may have to reboot it if it's been a long time since the last boot as what you may be looking is further back than the last 200 lines.