MD(4) Device Drivers Manual MD(4)

md
memory disk driver

pseudo-device md

The md driver enables use of system or user memory as a disk. Memory for the disk must be allocated within the kernel or with mdconfig(8) before the md device may be used as a disk. Its behaviour is configured by the kernel options MEMORY_DISK_HOOKS, MEMORY_DISK_IS_ROOT, MEMORY_DISK_ROOT_SIZE, MEMORY_DISK_DYNAMIC, and MEMORY_DISK_SERVER.

/dev/md??
block mode memory disk devices.
/dev/rmd??
raw mode memory disk devices.

options(4), mdconfig(8), mdsetimage(8)
November 30, 2013 NetBSD 9.4