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Example of a [.filename]#vinum#-based Root Setup
After the [.filename]#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 [.filename]#/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. [.filename]#/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 [.filename]#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 <<vinum-root-panic, Nothing Boots, the Bootstrap Panics>>. The entire `a` partition is completely within the `h` partition containing all the [.filename]#vinum# data for this device.
In the above example, the entire device is dedicated to [.filename]#vinum# and there is no leftover pre-[.filename]#vinum# root partition.
The following list contains a few known pitfalls and solutions.
System Bootstrap Loads, but System Does Not Boot
If for any reason the system does not continue to boot, the bootstrap can be interrupted by pressing kbd:[space] at the 10-seconds warning. The loader variable `vinum.autostart` can be examined by typing `show` and manipulated using `set` or `unset`.
If the [.filename]#vinum# kernel module was not yet in the list of modules to load automatically, type `load geom_vinum`.
When ready, the boot process can be continued by typing `boot -as` which `-as` requests the kernel to ask for the root file system to mount (`-a`) and make the boot process stop in single-user mode (`-s`), where the root file system is mounted read-only. That way, even if only one plex of a multi-plex volume has been mounted, no data inconsistency between plexes is being risked.
At the prompt asking for a root file system to mount, any device that contains a valid root file system can be entered. If [.filename]#/etc/fstab# is set up correctly, the default should be something like `ufs:/dev/gvinum/root`. A typical alternate choice would be something like `ufs:da0d` which could be a hypothetical partition containing the pre-[.filename]#vinum# root file system. Care should be taken if one of the alias `a` partitions is entered here, that it actually references the subdisks of the [.filename]#vinum# root device, because in a mirrored setup, this would only mount one piece of a mirrored root device. If this file system is to be mounted read-write later on, it is necessary to remove the other plex(es) of the [.filename]#vinum# root volume since these plexes would otherwise carry inconsistent data.
Only Primary Bootstrap Loads
If [.filename]#/boot/loader# fails to load, but the primary bootstrap still loads (visible by a single dash in the left column of the screen right after the boot process starts), an attempt can be made to interrupt the primary bootstrap by pressing kbd:[space]. This will make the bootstrap stop in link:{handbook}#boot-boot1[stage two]. An attempt can be made here to boot off an alternate partition, like the partition containing the previous root file system that has been moved away from `a`.
Nothing Boots, the Bootstrap Panics
This situation will happen if the bootstrap had been destroyed by the [.filename]#vinum# installation. Unfortunately, [.filename]#vinum# accidentally leaves only 4 KB at the beginning of its partition free before starting to write its [.filename]#vinum# header information. However, the stage one and two bootstraps plus the bsdlabel require 8 KB. So if a [.filename]#vinum# partition was started at offset 0 within a slice or disk that was meant to be bootable, the [.filename]#vinum# setup will trash the bootstrap.