SOFTRAID(4) BSD Kernel Interfaces Manual SOFTRAID(4)
softraid -- software RAID
softraid0 at root
The softraid device emulates a Host Bus Adapter (HBA) that provides RAID
and other I/O related services. The softraid device provides a scaffold
to implement more complex I/O transformation disciplines. For example,
one can tie chunks together into a mirroring discipline. There really is
no limit on what type of discipline one can write as long as it fits the
softraid supports a number of disciplines. A discipline is a collection
of functions that provides specific I/O functionality. This includes I/O
path, bring-up, failure recovery, and statistical information gathering.
Essentially a discipline is a lower level driver that provides the I/O
transformation for the softraid device.
A volume is a virtual disk device that is made up of a collection of
A chunk is a partition or storage area of fstype ``RAID''. disklabel(8)
is used to alter the fstype.
Currently softraid supports the following disciplines:
A striping discipline. It segments data over a number of chunks to
increase performance. RAID 0 does not provide for data loss
A mirroring discipline. It copies data across more than one chunk
to provide for data loss. Read performance is increased, though at
the cost of write speed. Unlike traditional RAID 1, softraid sup-
ports the use of more than two chunks in a RAID 1 setup.
An encrypting discipline. It encrypts data on a single chunk to
provide for data confidentiality. CRYPTO does not provide redun-
A concatenating discipline. It writes data to each chunk in
sequence to provide increased capacity. CONCAT does not provide
installboot(8) may be used to install boot(8) in the boot storage area of
the softraid volume. Boot support is currently limited to the CRYPTO and
RAID 1 disciplines on amd64, i386, and sparc64 platforms. On sparc64,
bootable chunks must be RAID partitions using the letter 'a'. At the
boot(8) prompt, softraid volumes have names beginning with 'sr' and can
be booted from like a normal disk device. CRYPTO volumes will require a
decryption passphrase or keydisk at boot time.
An example to create a 3 chunk RAID 1 from scratch is as follows:
Initialize the partition tables of all disks:
# fdisk -iy wd1
# fdisk -iy wd2
# fdisk -iy wd3
Now create RAID partitions on all disks:
# printf "a\n\n\n\nRAID\nw\nq\n\n" | disklabel -E wd1
# printf "a\n\n\n\nRAID\nw\nq\n\n" | disklabel -E wd2
# printf "a\n\n\n\nRAID\nw\nq\n\n" | disklabel -E wd3
Assemble the RAID volume:
# bioctl -c 1 -l /dev/wd1a,/dev/wd2a,/dev/wd3a softraid0
The console will show what device was added to the system:
scsibus0 at softraid0: 1 targets
sd0 at scsibus0 targ 0 lun 0: <OPENBSD, SR RAID 1, 001> SCSI2
sd0: 1MB, 0 cyl, 255 head, 63 sec, 512 bytes/sec, 3714 sec total
It is good practice to wipe the front of the disk before using it:
# dd if=/dev/zero of=/dev/rsd0c bs=1m count=1
Initialize the partition table and create a filesystem on the new RAID
# fdisk -iy sd0
# printf "a\n\n\n\n4.2BSD\nw\nq\n\n" | disklabel -E sd0
# newfs /dev/rsd0a
The RAID volume is now ready to be used as a normal disk device. See
bioctl(8) for more information on configuration of RAID sets.
Install boot(8) on the RAID volume:
# installboot sd0
At the boot(8) prompt, load the /bsd kernel from the RAID volume:
boot> boot sr0a:/bsd
bio(4), bioctl(8), boot_sparc64(8), disklabel(8), fdisk(8),
The softraid driver first appeared in OpenBSD 4.2.
The driver relies on underlying hardware to properly fail chunks.
The RAID 1 discipline does not initialize the mirror upon creation. This
is by design because all sectors that are read are written first. There
is no point in wasting a lot of time syncing random data.
Currently there is no automated mechanism to recover from failed disks.
Sparc hardware needs to use fstype ``4.2BSD'' instead of ``RAID''.
Certain RAID levels can protect against some data loss due to component
failure. RAID is not a substitute for good backup practices.
BSD April 29, 2017 BSD