Adding a new disk

Adding a new disk is relatively simple to a BSD system, However the most common way of adding a disk is through the USB subsystem. So I am trying to cover the two approaches here. Superficially the USB disk and the ‘normal’ disk just need to be ‘recognised’ - that is have a device file put in /dev/ with an appropraite driver.

Lets get to the point where a disk is recognised by dmesg.

Getting to dmesg

We can add a disk inside the PC as ‘normal’ - that is unscrew the covers and connect up a PATA (IDE) or SATA disk. In pretty much every case here, you will see that disk show up in dmesg

ad4: 57231MB <Hitachi HTS541660J9SA00 SBBOC70P> at ata2-master SATA150

So as expected I have a 60GB HDD on sata

However if I then plug in my USB enclosed external hard drive I see on Dmesg

umass0: <Maxtor OneTouch, class 0/0, rev 2.00/1.22, addr 2> on uhub2
da0 at umass-sim0 bus 0 target 0 lun 0
da0: <Maxtor OneTouch 0122> Fixed Direct Access SCSI-4 device
da0: 40.000MB/s transfers
da0: 114473MB (234441648 512 byte sectors: 255H 63S/T 14593C)

now this shows two things. FIrstly the umass driver. this is the USB-mass storage driver and it has found something on the USB Bus Then the driver is able to recognise the actual model, and so I have now got a device driver lined up and a ‘file’ sitting in /dev/da0

I can now use this as normal and proceed to the next step.

If umass discovers the disk but there is no device listed, frankly its tough. The drivers are not there and unless its vital, go buy another supported disk. See umass(8) for supported disks. There are loads, and given you can buy a 1TB for less than a hundred quid, its not worth worrying.

However if you really need that disk, try a firewire enclosure. This has less driver issues than USB.

Preparing and mounting the disk

  1. Zero the disk
  2. fdisk - Being nice to the PC BIOS
  3. bsdlabel - prepping for BSD
  4. newfs - writing the filesystems
  5. mount


zero the disk

This is straightforward dd from /dev/zero to your disk. I find that as a rough rule of thumb you can zero an entire 40GB disk in 20 minutes. [1]

#this overwrites the first 1024 bytes, effectviely killing the boot partition.
#leave off count to do the whole disk, make count 1000 to do first 1MB etc etc

dd if=/dev/zero of=/dev/da0 bs=1024 count=1


You do not have to do this, except for the boot disk iSo for a USB disk that is solely for backup, fine, used ‘dedicated’ mode

PC BIOS usually ‘controls’ a HDD. THat is it mediates the access from the OS to the BIOS to the HDD. THats how the PC was designed, and frankly BSD ignores it and can control the disk directly. However if BSD is controlling the disk directly, it cannot be used by some other OS that expects the BIOS to do the work. So BSD has ‘dedicated’ mode that means you use that disk only fafter BSD has booted - DOS wont like it, and BIOS wont boot from it.

a dedicated disk will look like /dev/da0e

We shall ignore that for now - the handbook recommends playing nice - using ‘slices’ A slice is a BSD term for one of the four BIOS partitions. so a BSD disk with 4 partitions will have device files called

/dev/ad4s1 /dev/ad4s2 /dev/ad4s3  /dev/ad4s4

Look at what is there

# fdisk -s /dev/ad4
/dev/ad4: 116280 cyl 16 hd 63 sec
Part        Start        Size Type Flags
   1:          63   117210177 0xa5 0x80

# fdisk /dev/ad4
******* Working on device /dev/ad4 *******
parameters extracted from in-core disklabel are:
cylinders=116280 heads=16 sectors/track=63 (1008 blks/cyl)

Figures below won't work with BIOS for partitions not in cyl 1
parameters to be used for BIOS calculations are:
cylinders=116280 heads=16 sectors/track=63 (1008 blks/cyl)

Media sector size is 512
Warning: BIOS sector numbering starts with sector 1
Information from DOS bootblock is:
The data for partition 1 is:
sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
    start 63, size 117210177 (57231 Meg), flag 80 (active)
        beg: cyl 0/ head 1/ sector 1;
        end: cyl 1023/ head 254/ sector 63
The data for partition 2 is:
The data for partition 3 is:
The data for partition 4 is:

this tells me that there are 4 slices or partitions, just as the BIOS expects, but that only one is initialised in a form readable to BIOS (ie the first partition, which the BIOS needs to read to boot the disk). The rest is handled by BSD itself, using infomration found in bsdlabel

So finally how to initialise my external USB hard disk to have slices the nice way

fdisk -BI /dev/da0
#this will
# -I Initialize sector 0 slice table for one FreeBSD slice covering the entire disk.
# -B Reinitialize the boot code contained in sector 0 of the disk

GEOM not found is considered a benign warning by the man file.


You will know have one slice on the disk, /dev/da0s1 This is generally what happens when you use sysinstall and just choose ‘use whole disk’


Here is where we create the traditional BSD partitions (not restrictive 4 BIOS paritions which are called slices now). The bsdlabel stores partition size and location info, as well as other stuff. it is read by BSD and used to control the HDD, bypassing the BIOS.

How do BSD partitions work? Basically there are eight partitions (a-h). (see

The a partition is solely for system disks (ie the disk you boot from). It is only used for the root (/) partition. The b partition is used for swap space. Any number of disks can have swap space, and the rule of thumb is to have twice RAM as swap. The c partition is a sort of whole disk placeholder

the e partition is usually the point to put /var in system disks and everything for other disks the f partition is usually the everything point (/usr) for system disks

-B will turn a slice into a bootable slice - by copying the boot code from
/boot/boot into the bootsector of the slice being worked on. It useful for system disks but this is not a system disk
#bsdlabel -w /dev/da0s1

OK this has built a standard label onto that slice. But it does not have our BSD partitions in it. we want swap, we want /usr etc. We get this by using

bsdlabel -e /dev/da0s1

this will use vi (EDITOR) to edit the label. Now a couple of points. firstly, use -n

bsdlabel -e -n /dev/da0s1

This will not write to the label, but do all calculations and output some hints for you. Second, the bsdlabel is good for calculating human-sized amounts

so when I freshly create the bsdlabel and use -e I get to see a label like this

# /dev/da0s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a: 234436466       16    unused        0     0
  c: 234436482        0    unused        0     0         # "raw" part, don't edit

The whole disk is taken up with the a partition which is OKish but not to convention.

I simply edit it using vi as follows

# /dev/da0s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 234436482        0    unused        0     0         # "raw" part, don't edit
  e: *                *    4.2BSD        0     0

I have told it to create a e: partition of ‘the whole remainder of the disk’ and it does the hard part for me.

Alternatives include

# /dev/da0s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a:       30G      16    4.2BSD        0     0
  b:        6G       *    swap
  c: 251658225       0    unused        0     0         # "raw" part, don't edit
  e:         *       *    4.2BSD        0     0

Building the file system

Now in the first example of editing the bsdlabel above, I have only created one partition so I only need one file system to be written on the partition. I just need to run

newfs -L BACKUP /dev/da0s1e

however with the second where it is looking a bit like a system disk

newfs -L ROOT /dev/da0s1a
#swap needs no filesystem
newfs -L USR /dev/da0s1e


# mkdir /mnt/disk1
# mount /dev/da0s1e /mnt/disk1


# dd if=/dev/zero of=/dev/da1 bs=1k count=1
# fdisk -BI da1 #Initialize your new disk
# bsdlabel -B -w da1s1 auto #Label it.
# bsdlabel -e da1s1 # Edit the bsdlabel just created and add any partitions.
# mkdir -p /1
# newfs /dev/da1s1e # Repeat this for every partition you created.
# mount /dev/da1s1e /1 # Mount the partition(s)
# vi /etc/fstab # Add the appropriate entry/entries to your /etc/fstab.

Actual results

[root@paullaptop ~]# dd if=/dev/zero of=/dev/da0 bs=1024 count=10
10+0 records in
10+0 records out
10240 bytes transferred in 0.208999 secs (48995 bytes/sec)

[root@paullaptop ~]# fdisk -BI /dev/da0
******* Working on device /dev/da0 *******
fdisk: invalid fdisk partition table found
fdisk: Geom not found: "da0"

Just format a USB Disk for use between BSD and Windows

In BSD-derived computer operating systems (including NetBSD,
OpenBSD, FreeBSD and DragonFly BSD) and in related operating
systems such as SunOS, a disklabel is a record stored on a data
storage device such as a hard disk that contains information about
the location of the partitions on the disk. Disklabels were
introduced in the 4.3BSD-Tahoe release.[1] Disklabels are usually
edited using the disklabel utility. In later versions of FreeBSD
this was renamed as bsdlabel.
[1]Will this be unreadable? Well yes, with caveats. Overwriting the disk with zeros once makes it unrecoverable except by scanning the surface of the disk with specialised equipment which can detect the tiny magnetic differences between a zero that was overwritten with zero and a one that was overwritten with zero. Unless you are a suspected terrorist or have stolen a billion dollars, overwriting with zeros once is fine. If you are a terrorist, firstly do not put your secret plans on a computer in the first place, secondly, use a masonary drill to destroy the platters, a few holes sufficient heat and presto, no recovery. Frankly this is all a bit academic. If you know the cops will get you in sufficient time for you to zero a disk or otherwise destroy it, the cops need to get better funding.
[2]In order for the BIOS to boot the kernel, certain conventions must be adhered to. Sector 0 of the disk must contain boot code, a slice table, and a magic number. BIOS slices can be used to break the disk up into several pieces. The BIOS brings in sector 0 and verifies the magic num- ber. The sector 0 boot code then searches the slice table to determine which slice is marked ``active’‘. This boot code then brings in the bootstrap from the active slice and, if marked bootable, runs it. Under DOS, you can have one or more slices with one active. The DOS fdisk utility can be used to divide space on the disk into slices and set one active.