1.\" ---------------------------------------------------------------------------- 2.\" "THE BEER-WARE LICENSE" (Revision 42): 3.\" <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you 4.\" can do whatever you want with this stuff. If we meet some day, and you think 5.\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp 6.\" ---------------------------------------------------------------------------- 7.\" 8.\" $FreeBSD$ 9.\" 10.Dd March 9, 2001 11.Dt MD 4 12.Os 13.Sh NAME 14.Nm md 15.Nd memory disk 16.Sh SYNOPSIS 17.Cd device md 18.Sh DESCRIPTION 19The 20.Nm 21driver provides support for four kinds of memory backed virtual disks: 22.Bl -tag -width preload 23.It Cm malloc 24Backing store is allocated using 25.Xr malloc 9 . 26Only one malloc-bucket is used, which means that all 27.Nm 28devices with 29.Cm malloc 30backing must share the malloc-per-bucket-quota. 31The exact size of this quota varies, in particular with the amount 32of RAM in the 33system. 34The exact value can be determined with 35.Xr vmstat 8 . 36.It Cm preload 37A file loaded by 38.Xr loader 8 39with type 40.Sq md_image 41is used for backing store. 42For backwards compatibility the type 43.Sq mfs_root 44is also recognized. 45If the kernel is created with option 46.Dv MD_ROOT 47the first preloaded image found will become the root filesystem. 48.It Cm vnode 49A regular file is used as backing store. 50This allows for mounting ISO images without the tedious 51detour over actual physical media. 52.It Cm swap 53Backing store is allocated from swap space. 54.El 55.Pp 56For more information, please see 57.Xr mdconfig 8 . 58.Sh SEE ALSO 59.Xr disklabel 5 , 60.Xr disklabel 8 , 61.Xr fdisk 8 , 62.Xr loader 8 , 63.Xr mdconfig 8 , 64.Xr newfs 8 , 65.Xr vmstat 8 66.Sh HISTORY 67The 68.Nm 69driver first appeared in 70.Fx 4.0 71as a cleaner replacement 72for the MFS functionality previously used in 73.Tn PicoBSD 74and in the 75.Fx 76installation process. 77.Pp 78The 79.Nm 80driver did a hostile takeover of the 81.Xr vn 4 82driver in 83.Fx 5.0 . 84.Sh AUTHORS 85The 86.Nm 87driver was written by 88.An Poul-Henning Kamp 89.Aq phk@FreeBSD.org . 90