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.\" $OpenBSD: softraid.4,v 1.8 2007/05/31 02:49:05 grunk Exp $
.\"
.\" Copyright (c) 2007 Todd T. Fries <todd@OpenBSD.org>
.\" Copyright (c) 2007 Marco Peereboom <marco@OpenBSD.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd March 19, 2007
.Dt SOFTRAID 4
.Os
.Sh NAME
.Nm softraid
.Nd Software RAID
.Sh SYNOPSIS
.Cd "softraid0 at root"
.Cd "scsibus* at softraid?"
.Sh DESCRIPTION
The
.Nm
device emulates an HBA 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).
.Pp
Currently
.Nm
only supports a mirroring discipline.
.Pp
A
.Em discipline
is a collection of functions that provides specific IO
functionality.
This includes IO path, bring-up, failure recovery, statistical
information gathering etc.\&
Essentially a discipline is a lower
level driver that provides the IO transformation for the softraid
device.
.Pp
A
.Em volume
is a virtual disk device that is made up of a collection of chunks.
.Pp
A
.Em chunk
is a partition or storage area of the type RAID.
.Sh EXAMPLES
The first step to using the
.Nm
driver is to ensure that it is suitably configured in the kernel.
This is done by uncommenting the softraid device in
.Pa sys/conf/GENERIC
and recompiling it.
Uncomment the following lines:
.Bd -literal -offset indent
#softraid0 at root # Software RAID
#scsibus* at softraid?
.Ed
.Pp
An example to create a 3 chunk RAID 1 from scratch is as follows:
.Pp
Initialize the partition tables of all disks:
.Bd -literal -offset indent
echo y | fdisk -i wd1
echo y | fdisk -i wd2
echo y | fdisk -i wd3
.Ed
.Pp
Now create RAID partitions on all disks:
.Bd -literal -offset indent
echo "d a\ena\en\en\en\enRAID\enw\enq\en" | disklabel -E wd1
echo "d a\ena\en\en\en\enRAID\enw\enq\en" | disklabel -E wd2
echo "d a\ena\en\en\en\enRAID\enw\enq\en" | disklabel -E wd3
.Ed
.Pp
Assemble the RAID volume:
.Bd -literal -offset indent
bioctl -c 1 -l /dev/wd1a,/dev/wd2a,/dev/wd3a softraid0
.Ed
.Pp
The console will give away what device was added to the system:
.Bd -literal -offset indent
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
.Ed
.Pp
It is good practice to wipe the front of the disk before using it:
.Bd -literal -offset indent
dd if=/dev/zero of=/dev/rsd0c bs=1m count=1
.Ed
.Pp
Initialize the partition table and create a filesystem on the
new RAID volume:
.Bd -literal -offset indent
echo y | fdisk -i sd0
echo "d a\ena\en\en\en\en4.2BSD\enw\enq\en" | disklabel -E sd0
newfs /dev/rsd0a
.Ed
.Pp
The RAID volume is now ready to be used as a normal disk device.
.Pp
See
.Xr bioctl 8
for more information on configuration of RAID sets.
.Pp
All component partitions must be of type
.Dv RAID .
Some platforms, such as SUN, are not capable of using the
.Dv RAID
partition type.
The
.Dv 4.2BSD
partition type should be used on such platforms.
.Sh SEE ALSO
.Xr sd 4 ,
.Xr wd 4 ,
.Xr bioctl 8 ,
.Xr config 8 ,
.Xr fsck 8 ,
.Xr MAKEDEV 8 ,
.Xr mount 8 ,
.Xr newfs 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 4.2 .
.Sh AUTHORS
.An Marco Peereboom .
.Sh CAVEATS
The driver relies on underlying hardware to properly fail chunks.
Currently the RAID 1 support does not have the ability to recover a
failed chunk.
.Pp
The RAID 1 discipline does not initialize the mirror upon creation.
.Pp
Certain RAID levels can protect against some data loss
due to component failure.
RAID is
.Em not
a substitute for good backup practices.
|
