SOFTRAID(4) OpenBSD Programmer's Manual SOFTRAID(4)
NAME
softraid - Software RAID
SYNOPSIS
softraid0 at root
scsibus* at softraid?
DESCRIPTION
The softraid device emulates an HBA (host bus adapter) that provides RAID
and other IO related services. The idea is to tie chunks together into
an IO discipline. A discipline can for example provide a volume that
mirrors chunks (RAID 1).
Currently softraid only supports a mirroring discipline.
A discipline is a collection of functions that provides specific IO func-
tionality. This includes IO path, bring-up, failure recovery, statisti-
cal information gathering etc. Essentially a discipline is a lower level
driver that provides the IO transformation for the softraid device.
A volume is a virtual disk device that is made up of a collection of
chunks.
A chunk is a partition or storage area of the type RAID.
EXAMPLES
An example to create a 3 chunk RAID 1 from scratch is as follows:
Initialize the partition tables of all disks:
echo y | fdisk -i wd1
echo y | fdisk -i wd2
echo y | fdisk -i wd3
Now create RAID partitions on all disks:
echo "d a\na\n\n\n\nRAID\nw\nq\n" | disklabel -E wd1
echo "d a\na\n\n\n\nRAID\nw\nq\n" | disklabel -E wd2
echo "d a\na\n\n\n\nRAID\nw\nq\n" | disklabel -E wd3
Assemble the RAID volume:
bioctl -c 1 -l /dev/wd1a,/dev/wd2a,/dev/wd3a softraid0
The console will give away 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
volume:
echo y | fdisk -i sd0
echo "d a\na\n\n\n\n4.2BSD\nw\nq\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.
All component partitions must be of type RAID. Some platforms, such as
SUN, are not capable of using the RAID partition type. The 4.2BSD parti-
tion type should be used on such platforms.
SEE ALSO
sd(4), wd(4), bioctl(8), config(8), fsck(8), MAKEDEV(8), mount(8),
newfs(8)
HISTORY
The softraid driver first appeared in OpenBSD 4.2.
AUTHORS
Marco Peereboom.
CAVEATS
The driver relies on underlying hardware to properly fail chunks. Cur-
rently the RAID 1 support does not have the ability to recover a failed
chunk.
The RAID 1 discipline does not initialize the mirror upon creation.
Certain RAID levels can protect against some data loss due to component
failure. RAID is not a substitute for good backup practices.
OpenBSD 4.2 June 2, 2007 2