vinum must be available early in the system boot as loader(8) must be able to load the vinum kernel module before starting the kernel. This can be accomplished by putting this line in /boot/loader.conf:

geom_vinum_load="YES"

The current FreeBSD bootstrap is only 7.5 KB of code and does not understand the internal vinum structures. This means that it cannot parse the vinum configuration data or figure out the elements of a boot volume. Thus, some workarounds are necessary to provide the bootstrap code with the illusion of a standard a partition that contains the root file system.

For this to be possible, the following requirements must be met for the root volume:

Note that it is desirable and possible to use multiple plexes, each containing one replica of the root file system. The bootstrap process will only use one replica for finding the bootstrap and all boot files, until the kernel mounts the root file system. Each single subdisk within these plexes needs its own a partition illusion, for the respective device to be bootable. It is not strictly needed that each of these faked a partitions is located at the same offset within its device, compared with other devices containing plexes of the root volume. However, it is probably a good idea to create the vinum volumes that way so the resulting mirrored devices are symmetric, to avoid confusion.

In order to set up these a partitions for each device containing part of the root volume, the following is required:

It should be remembered that all files containing control information must be relative to the root file system in the vinum volume which, when setting up a new vinum root volume, might not match the root file system that is currently active. So in particular, /etc/fstab and /boot/loader.conf need to be taken care of.

At next reboot, the bootstrap should figure out the appropriate control information from the new vinum-based root file system, and act accordingly. At the end of the kernel initialization process, after all devices have been announced, the prominent notice that shows the success of this setup is a message like:

Mounting root from ufs:/dev/gvinum/root

After the vinum root volume has been set up, the output of gvinum l -rv root could look like:

...
Subdisk root.p0.s0:
		Size:        125829120 bytes (120 MB)
		State: up
		Plex root.p0 at offset 0 (0  B)
		Drive disk0 (/dev/da0h) at offset 135680 (132 kB)

Subdisk root.p1.s0:
		Size:        125829120 bytes (120 MB)
		State: up
		Plex root.p1 at offset 0 (0  B)
		Drive disk1 (/dev/da1h) at offset 135680 (132 kB)

The values to note are 135680 for the offset, relative to partition /dev/da0h. This translates to 265 512-byte disk blocks in bsdlabel's terms. Likewise, the size of this root volume is 245760 512-byte blocks. /dev/da1h, containing the second replica of this root volume, has a symmetric setup.

The bsdlabel for these devices might look like:

...
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a:   245760      281    4.2BSD     2048 16384     0   # (Cyl.    0*- 15*)
  c: 71771688        0    unused        0     0         # (Cyl.    0 - 4467*)
  h: 71771672       16     vinum                        # (Cyl.    0*- 4467*)

It can be observed that the size parameter for the faked a partition matches the value outlined above, while the offset parameter is the sum of the offset within the vinum partition h, and the offset of this partition within the device or slice. This is a typical setup that is necessary to avoid the problem described in Section 8.4.3, “Nothing Boots, the Bootstrap Panics”. The entire a partition is completely within the h partition containing all the vinum data for this device.

In the above example, the entire device is dedicated to vinum and there is no leftover pre-vinum root partition.

The following list contains a few known pitfalls and solutions.