diff --git a/share/man/man4/md.4 b/share/man/man4/md.4 index ea783610c6fb..fc3c84619570 100644 --- a/share/man/man4/md.4 +++ b/share/man/man4/md.4 @@ -15,102 +15,46 @@ .Nd memory disk .Sh SYNOPSIS .Cd device md -.Pp -To specify the default maximum size of -.Xr malloc 9 -backed disks: -.Cd options MD_NSECT=20000 .Sh DESCRIPTION The .Nm -driver provides support for two kinds of memory backed virtual disks: -.Xr malloc 9 -backed -and pre-loaded module backed. -.Pp -The -.Xr malloc 9 -backed -disks -are severely limited in size by constraints imposed by +driver provides support for four kinds of memory backed virtual disks: +.Bl -tag -width preload +.It Cm malloc +Backing store is allocated using .Xr malloc 9 . -The limit imposed depends on the amount of physical RAM in the machine, -and covers all -.Xr malloc 9 -backed instances of +Only one malloc-bucket is used, which means that all .Nm -devices. -.Pp -A sector filled with identical bytes does not consume storage, -and therefore the storage allocated by a -.Nm -disk can be freed with a command such as this: -.Bd -literal -offset indent -dd if=/dev/zero of=/dev/md567 -.Ed -.Pp -The default maximum size of a -.Nm -disk -backed by -.Xr malloc 9 -is 20,000 sectors of 512 bytes each. -This can be changed -with the kernel option -.Dv MD_NSECT . -.Pp -At boot time the -.Nm -driver will search for pre-loaded modules of type +devices with +.Cm malloc +backing must share the malloc-per-bucket-quota. +The exact size of this quota varies, in particular with amount of RAM in the +system. The exact value can be determined with +.Xr vmstat 8 . +.It Cm preload +A file loaded by +.Xr loader 8 +with type .Sq md_image -and instantiate a -.Nm -device for each of these modules. -The type +is used for backing store. +For backwards compatibility the type .Sq mfs_root -is also allowed for backward compatibility. -These devices are backed by the RAM reserved by the -.Xr loader 8 , -and as such not limited by the -.Xr malloc 9 -size constraints. -However, this also means that the storage cannot be released. -For the same reason, -the -.Dq identical byte -detection is not applicable. +is also recognized. +If the kernel is created with option +.Cm MD_ROOT +the first preloaded image found will become the root filesystem. +.It Cm vnode +A regular file is used as backing store. +This allows for mounting ISO images without the tedious +detour over actual physical media. +.It Cm swap +Backing store is allocated from swap space. +.El .Pp -The -.Nm -driver uses the -.Dq almost-clone -convention, -whereby opening device number N creates device instance number N+1. -.Pp -The -.Xr vmstat 8 -utility can be used to monitor memory usage by -.Xr malloc 9 -backed -.Nm -disks, -but not those backed by pre-loaded modules. -.Sh EXAMPLES -To mount a -.Xr malloc 9 -backed -.Nm -device on -.Pa /tmp : -.Bd -literal -if [ -e /dev/md0 -a -e /dev/md0c ]; then - disklabel -r -w md0 auto && \\ - newfs /dev/md0c && \\ - mount /dev/md0c /tmp && \\ - chmod 1777 /tmp -fi -.Ed +For more information, please see +.Xr mdconfig 8 .Sh SEE ALSO +.Xr mdconfig 8 , .Xr disklabel 5 , .Xr disklabel 8 , .Xr fdisk 8 , @@ -127,6 +71,13 @@ for the MFS functionality previously used in PicoBSD and in the .Fx installation process. +.Pp +The +.Nm +driver did a hostile takeover of the +.Xr vn 4 +driver in +.Fx 5.0 . .Sh AUTHORS The .Nm