1.\" 2.\" Copyright (c) 2006 Wilko Bulte 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\"
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26.\" $FreeBSD: head/share/man/man4/geom_fox.4 206622 2010-04-14 19:08:06Z uqs $
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26.\" $FreeBSD: head/share/man/man4/geom_fox.4 208027 2010-05-13 12:07:55Z uqs $ |
27.\" 28.Dd January 2, 2005 29.Dt GEOM_FOX 4 30.Os 31.Sh NAME 32.Nm geom_fox 33.Nd "GEOM based basic disk multipathing" 34.Sh SYNOPSIS 35To compile this driver into the kernel, 36place the following line in your 37kernel configuration file: 38.Bd -ragged -offset indent 39.Cd "options GEOM_FOX" 40.Ed 41.Pp 42Alternatively, to load the driver as a 43module at boot time, place the following line in 44.Xr loader.conf 5 : 45.Bd -literal -offset indent 46geom_fox_load="YES" 47.Ed 48.Sh DESCRIPTION 49The intent of the 50.Nm 51framework is to provide basic multipathing support to access direct 52access devices. 53Basic in the above sentence should be read as: 54.Nm 55only provides path failover functionality, not load balancing over 56the available paths etc. 57Using suitable hardware like SCSI or FibreChannel disks it is 58possible to have multiple (typically 2) host bus adapters access 59the same physical disk drive. 60.Pp 61Without a multipathing driver the 62.Fx 63kernel would probe the disks multiple times, resulting in the creation of 64multiple 65.Pa /dev 66entries for the same underlying physical device. 67A unique label written in the GEOM label area allows 68.Nm 69to detect multiple paths. 70Using this information it creates a unique 71.Pa da#.fox 72device. 73.Pp 74The 75.Nm 76device is subsequently used by the 77.Fx 78kernel to access the disks. 79Multiple physical access paths ensure that even in case of a path failure the 80.Fx 81kernel can continue to access the data. 82.Pp 83The 84.Nm 85driver will disallow write operations to the underlying devices once the 86fox device has been opened for writing. 87.Sh EXAMPLES 88.Pp 89.Bl -bullet -compact 90.It 91.Nm 92needs a label on the disk as follows in order to work properly: 93.Bd -literal 94"0123456789abcdef0123456789abcdef" 95"GEOM::FOX <--unique--id-->" 96.Ed 97.Pp 98For the unique ID 16 bytes are available. 99The 100.Dq Li GEOM::FOX 101is the magic to mark a 102.Nm 103device. 104.Pp 105The actual labelling is accomplished by 106.Bd -literal 107echo "GEOM::FOX someid" | dd of=/dev/da2 conv=sync 108.Ed 109.Pp 110For FibreChannel devices it is suggested to use the Node World Wide 111Name (Node WWN) as this is guaranteed by the FibreChannel standard to 112be worldwide unique. 113The use of the Port WWN not recommended as each port of a given 114device has a different WWN, thereby confusing things. 115.Pp 116The Node WWN can be obtained from a verbose boot as in for example 117.Bd -literal 118isp1: Target 1 (Loop 0x1) Port ID 0xe8 (role Target) Arrived 119 Port WWN 0x21000004cfc8aca2 120 Node WWN 0x20000004cfc8aca2 121.Ed 122.Pp 123This Node WWN would then be used like so: 124.Bd -literal 125echo "GEOM::FOX 20000004cfc8aca2" | dd of=/dev/da2 conv=sync 126.Ed 127.Pp 128For non-FibreChannel devices you could for example use the serial 129number of the device. 130Regardless of what you use, make sure the label is unique. 131.Pp 132Once the labelling has been performed and assuming the 133.Nm 134module is loaded the kernel will inform you that it has found a new 135.Nm 136device with a message similar to 137.Bd -literal 138Creating new fox (da2) 139fox da2.fox lock 0xfffffc0000fdba20 140.Ed 141.Pp 142.It 143To check which physical devices match a given 144.Nm 145device: 146.Bd -literal -offset indent 147# geom fox list 148Geom name: da2.fox 149Providers: 1501. Name: da2.fox 151 Mediasize: 73407865344 (68G) 152 Sectorsize: 512 153 Mode: r0w0e0 154Consumers: 1551. Name: da2 156 Mediasize: 73407865856 (68G) 157 Sectorsize: 512 158 Mode: r0w0e0 1592. Name: da6 160 Mediasize: 73407865856 (68G) 161 Sectorsize: 512 162 Mode: r0w0e0 163.Ed 164.Pp 165.It 166To check the status of the 167.Nm 168components: 169.Bd -literal 170# geom fox status 171 Name Status Components 172da2.fox N/A da2 173 da6 174.Ed 175.El 176.Sh SEE ALSO 177.Xr GEOM 4 , 178.Xr geom 8 , 179.Xr gmultipath 8
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180.Sh AUTHORS 181.An -nosplit 182The 183.Nm 184driver was written by 185.An "Poul-Henning Kamp" Aq phk@FreeBSD.org . 186This manual page was written by 187.An "Wilko Bulte" Aq wilko@FreeBSD.org . |
188.Sh CAVEATS 189The 190.Nm 191driver depends on the underlying hardware drivers to do the right thing in case 192of a path failure. 193If for example a hardware driver continues to retry forever, 194.Nm 195is not able to re-initiate the I/O to an alternative physical path. 196.Pp 197You have to be very sure to provide a unique label for each of the 198.Nm 199devices. 200Safety belts are not provided. 201For FibreChannel devices it is suggested to use the Port WWN of the device. 202The World Wide Name is guaranteed to be worldwide unique per the 203FibreChannel standard.
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196.Sh AUTHORS
197.An -nosplit
198The
199.Nm
200driver was written by
201.An "Poul-Henning Kamp" Aq phk@FreeBSD.org .
202This manual page was written by
203.An "Wilko Bulte" Aq wilko@FreeBSD.org .
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204.Sh BUGS 205The 206.Nm 207framework has only seen light testing. 208There definitely might be dragons here. 209.Pp 210The name 211.Nm 212is completely obscure. 213Just remember that any sly fox has multiple exits from its hole. 214.Pp 215The examples provided are too FibreChannel-centric.
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