1.\" $OpenBSD: softraid.4,v 1.18 2008/06/14 00:16:38 hshoexer Exp $ 2.\" 3.\" Copyright (c) 2007 Todd T. Fries <todd@OpenBSD.org> 4.\" Copyright (c) 2007 Marco Peereboom <marco@OpenBSD.org> 5.\" 6.\" Permission to use, copy, modify, and distribute this software for any 7.\" purpose with or without fee is hereby granted, provided that the above 8.\" copyright notice and this permission notice appear in all copies. 9.\" 10.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 11.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 12.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 13.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 14.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 15.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 16.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 17.\" 18.Dd $Mdocdate: June 14 2008 $ 19.Dt SOFTRAID 4 20.Os 21.Sh NAME 22.Nm softraid 23.Nd Software RAID 24.Sh SYNOPSIS 25.Cd "softraid0 at root" 26.Cd "scsibus* at softraid?" 27.Sh DESCRIPTION 28The 29.Nm 30device emulates a Host Bus Adapter (HBA) that provides RAID and other I/O 31related services. 32The 33.Nm 34device provides a scaffold to implement more complex I/O transformation 35disciplines. 36For example, one can tie chunks together into a mirroring discipline. 37There really is no limit on what type of discipline one can write as long 38as it fits the SCSI model. 39.Pp 40.Nm 41supports a number of 42.Em disciplines . 43A discipline is a collection of functions 44that provides specific I/O functionality. 45This includes I/O path, bring-up, failure recovery, statistical 46information gathering etc.\& 47Essentially a discipline is a lower 48level driver that provides the I/O transformation for the softraid 49device. 50.Pp 51Currently 52.Nm 53supports the following disciplines: 54.Bl -ohang -offset indent 55.It RAID 0 56A 57.Em striping 58discipline. 59It segments data over a number of disks to increase performance. 60RAID 0 does not provide for data loss (redundancy). 61.It RAID 1 62A 63.Em mirroring 64discipline. 65It copies data across more than one disk to provide for data loss. 66Read performance is increased, 67though at the cost of write speed. 68Unlike traditional RAID 1, 69.Nm 70supports the use of more than two disks in a RAID 1 setup. 71.It CRYPTO 72An 73.Em encrypting 74discipline. 75It encrypts data on a single disk to provide for data confidentiality. 76CRYPTO does not provide redundancy. 77.El 78.Pp 79A 80.Em volume 81is a virtual disk device that is made up of a collection of chunks. 82.Pp 83A 84.Em chunk 85is a partition or storage area of the type RAID. 86.Sh EXAMPLES 87An example to create a 3 chunk RAID 1 from scratch is as follows: 88.Pp 89Initialize the partition tables of all disks: 90.Bd -literal -offset indent 91# fdisk -iy wd1 92# fdisk -iy wd2 93# fdisk -iy wd3 94.Ed 95.Pp 96Now create RAID partitions on all disks: 97.Bd -literal -offset indent 98# printf "a\en\en\en\enRAID\enw\enq\en\en" | disklabel -E wd1 99# printf "a\en\en\en\enRAID\enw\enq\en\en" | disklabel -E wd2 100# printf "a\en\en\en\enRAID\enw\enq\en\en" | disklabel -E wd3 101.Ed 102.Pp 103Assemble the RAID volume: 104.Bd -literal -offset indent 105# bioctl -c 1 -l /dev/wd1a,/dev/wd2a,/dev/wd3a softraid0 106.Ed 107.Pp 108The console will show what device was added to the system: 109.Bd -literal -offset indent 110scsibus0 at softraid0: 1 targets 111sd0 at scsibus0 targ 0 lun 0: <OPENBSD, SR RAID 1, 001> SCSI2 112sd0: 1MB, 0 cyl, 255 head, 63 sec, 512 bytes/sec, 3714 sec total 113.Ed 114.Pp 115It is good practice to wipe the front of the disk before using it: 116.Bd -literal -offset indent 117# dd if=/dev/zero of=/dev/rsd0c bs=1m count=1 118.Ed 119.Pp 120Initialize the partition table and create a filesystem on the 121new RAID volume: 122.Bd -literal -offset indent 123# fdisk -iy sd0 124# printf "a\en\en\en\en4.2BSD\enw\enq\en\en" | disklabel -E sd0 125# newfs /dev/rsd0a 126.Ed 127.Pp 128The RAID volume is now ready to be used as a normal disk device. 129.Pp 130See 131.Xr bioctl 8 132for more information on configuration of RAID sets. 133.Pp 134All component partitions must be of type 135.Dv RAID . 136Some platforms, such as SUN, are not capable of using the 137.Dv RAID 138partition type. 139The 140.Dv 4.2BSD 141partition type should be used on such platforms. 142.Sh SEE ALSO 143.Xr sd 4 , 144.Xr wd 4 , 145.Xr bioctl 8 , 146.Xr config 8 , 147.Xr fsck 8 , 148.Xr MAKEDEV 8 , 149.Xr mount 8 , 150.Xr newfs 8 151.Sh HISTORY 152The 153.Nm 154driver first appeared in 155.Ox 4.2 . 156.Sh AUTHORS 157.An Marco Peereboom . 158.Sh CAVEATS 159The driver relies on underlying hardware to properly fail chunks. 160Currently RAID 1 support does not have the ability to recover a 161failed chunk. 162.Pp 163The RAID 1 discipline does not initialize the mirror upon creation. 164This is by design because all sectors that are read are written first. 165There is no point in wasting a lot of time syncing random data. 166.Pp 167Currently there is no automated mechanism to recover from failed disks. 168.Pp 169There is no boot support at this time for any disciplines. 170.Pp 171Certain RAID levels can protect against some data loss 172due to component failure. 173RAID is 174.Em not 175a substitute for good backup practices. 176