## 12.11 Network, Memory, and File-Backed File Systems 

***Reorganized and enhanced by Marc Fonvieille. ***

Aside from the disks you physically insert into your computer: floppies, CDs, hard drives, and so forth; other forms of disks are understood by DragonFly - the ***virtual disks***.

These include network file systems such as the [network-nfs.html Network File System], memory-based file systems and file-backed file systems.

### 12.11.1 File-Backed File System 

The utility [vnconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#vnconfig&section8) configures and enables vnode pseudo-disk devices. A ***vnode*** is a representation of a file, and is the focus of file activity. This means that [vnconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=vnconfig&section=8) uses files to create and operate a file system. One possible use is the mounting of floppy or CD images kept in files.

To use [vnconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#vnconfig&section8), you need [vn(4)](http://leaf.dragonflybsd.org/cgi/web-man?command=vn&section=4) support in your kernel configuration file:

    
    pseudo-device vn


To mount an existing file system image:

 **Example 12-4. Using vnconfig to Mount an Existing File System Image** 

    
    # vnconfig vn`***0***` `***diskimage***`
    # mount /dev/vn`***0***`c `***/mnt***`


To create a new file system image with [vnconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#vnconfig&section8):

 **Example 12-5. Creating a New File-Backed Disk with `vnconfig`** 

    
    # dd if#/dev/zero of`***newimage***` bs=1k count=`***5***`k
    5120+0 records in
    5120+0 records out
    # vnconfig -s labels -c vn`***0***` `***newimage***`
    # disklabel -r -w vn`***0***` auto
    # newfs vn`***0***`c
    Warning: 2048 sector(s) in last cylinder unallocated
    /dev/vn0c:     10240 sectors in 3 cylinders of 1 tracks, 4096 sectors
            5.0MB in 1 cyl groups (16 c/g, 32.00MB/g, 1280 i/g)
    super-block backups (for fsck -b #) at:
     32
    # mount /dev/vn`***0***`c `***/mnt***`
    # df `***/mnt***`
    Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
    /dev/vn0c        4927        1     4532     0%    /mnt


### 12.11.2 Memory-Based File System 

The [md(4)](http://leaf.dragonflybsd.org/cgi/web-man?command#md&section4) driver is a simple, efficient means to create memory file systems. [malloc(9)](http://leaf.dragonflybsd.org/cgi/web-man?command=malloc&section=9) is used to allocate the memory.

Simply take a file system you have prepared with, for example, [vnconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#vnconfig&section8), and:

 **Example 12-6. md Memory Disk** 

    
    # dd if#`***newimage***` of/dev/md`***0***`
    5120+0 records in
    5120+0 records out
    # mount /dev/md`***0c***` `***/mnt***`
    # df `***/mnt***`
    Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
    /dev/md0c        4927        1     4532     0%    /mnt


For more details, please refer to [md(4)](http://leaf.dragonflybsd.org/cgi/web-man?command#md&section4) manual page.

### 12.11.3 Detaching a Memory Disk from the System 

When a memory-based or file-based file system is not used, you should release all resources to the system. The first thing to do is to unmount the file system, then use [mdconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#mdconfig&section8) to detach the disk from the system and release the resources.

For example to detach and free all resources used by `/dev/md4`:

    
    # mdconfig -d -u `***4***`


It is possible to list information about configured [md(4)](http://leaf.dragonflybsd.org/cgi/web-man?command#md&section4) devices in using the command `mdconfig -l`.

[vnconfig(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#vnconfig&section8) is used to detach the device. For example to detach and free all resources used by `/dev/vn4`:

    
    # vnconfig -u vn`***4***`




CategoryHandbook
CategoryHandbook-storage