---
name: "vn"
section: "4"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux"]
url: "https://new.carta.tech/vn"
---

# vn(4)

memory disk

## NAME

**md** – memory disk

## SYNOPSIS

**device** **md**

## DESCRIPTION

The **md** driver provides support for four kinds of memory backed virtual disks:

- **malloc**

  Backing store is allocated using [malloc(9)](/malloc/9.md). Only one malloc-bucket is used, which means that all **md** devices with **malloc** backing must share the malloc-per-bucket-quota. The exact size of this quota varies, in particular with the amount of RAM in the system. The exact value can be determined with [vmstat(8)](/vmstat/8.md).

- **preload**

  A file loaded by [loader(8)](/loader/8.md) with type ‘md\_image’ is used for backing store. For backwards compatibility the type ‘mfs\_root’ is also recognized. If the kernel is created with option MD\_ROOT the first preloaded image found will become the root file system.

- **vnode**

  A regular file is used as backing store. This allows for mounting ISO images without the tedious detour over actual physical media.

- **swap**

  Backing store is allocated from swap space.

For more information, please see [mdconfig(8)](/mdconfig/8.md).

## SEE ALSO

[disklabel(5)](/disklabel/5.md), [disklabel(8)](/disklabel/8.md), [fdisk(8)](/fdisk/8.md), [loader(8)](/loader/8.md), [mdconfig(8)](/mdconfig/8.md), [mdmfs(8)](/mdmfs/8.md), [newfs(8)](/newfs/8.md), [vmstat(8)](/vmstat/8.md)

## HISTORY

The **md** driver first appeared in FreeBSD 4.0 as a cleaner replacement for the MFS functionality previously used in PicoBSD and in the FreeBSD installation process.

The **md** driver did a hostile takeover of the [vn(4)](/vn/4.md) driver in FreeBSD 5.0.

## AUTHORS

The **md** driver was written by Poul-Henning Kamp ⟨phk@FreeBSD.org⟩.