Hitchhiker's Guide to Openbsd

Auto-partitioning: New users are encouraged to use the 'A' command to auto-create a recommended 
disklabel. You can then edit or alter the auto-created label as you need. 
14.4 - Adding extra disks in OpenBSD
http://www.openbsd.org/faq/faq14.html (8 of 34)9/4/2011 10:02:25 AM

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14 - Disk Setup
Well once you get your disk installed PROPERLY you need to use 
fdisk(8)
 (i386 only) and 
disklabel(8)
 to set up 
your disk in OpenBSD. 
For i386 folks, start with fdisk. Other architectures can ignore this. In the below example we're adding a third 
SCSI drive to the system. 
# fdisk -i sd2
This will initialize the disk's "real" partition table for exclusive use by OpenBSD. Next you need to create a 
disklabel for it. This will seem confusing. 
# disklabel -e sd2
(screen goes blank, your $EDITOR comes up)
type: SCSI
...bla...
sectors/track: 63
total sectors: 6185088
...bla...
16 partitions:
# size offset fstype [fsize bsize cpg]
c: 6185088 0 unused 0 0 # (Cyl.
0 - 6135)
d: 1405080 63 4.2BSD 1024 8192 16 # (Cyl.
0*- 1393*)
e: 4779945 1405143 4.2BSD 1024 8192 16 # (Cyl. 
1393*- 6135)
First, ignore the 'c' partition, it's always there and is for programs like disklabel to function! Fstype for OpenBSD 
is 4.2BSD. Total sectors is the total size of the disk. Say this is a 3 gigabyte disk. Three gigabytes in disk 
manufacturer terms is 3000 megabytes. So divide 6185088/3000 (use 
bc(1)
). You get 2061. So, to make up 
partition sizes for a, d, e, f, g, ... just multiply X*2061 to get X megabytes of space on that partition. The offset for 
your first new partition should be the same as the "sectors/track" reported earlier in disklabel's output. For us it is 
63. The offset for each partition afterwards should be a combination of the size of each partition and the offset of 
each partition (except the 'c' partition, since it has no play into this equation.) 
Or, if you just want one partition on the disk, say you will use the whole thing for web storage or a home directory 
or something, just take the total size of the disk and subtract the sectors per track from it. 6185088-63 = 6185025. 
Your partition is 
d: 6185025 63 4.2BSD 1024 8192 16