2 .\" Copyright (c) 2006 Wilko Bulte
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28 .Dd September 12, 2015
33 .Nd "GEOM based basic disk multipathing"
35 To compile this driver into the kernel,
36 place the following line in your
37 kernel configuration file:
38 .Bd -ragged -offset indent
39 .Cd "options GEOM_FOX"
42 Alternatively, to load the driver as a
43 module at boot time, place the following line in
45 .Bd -literal -offset indent
50 This driver is obsolete.
51 Users are advised to use
58 framework is to provide basic multipathing support to access direct
60 Basic in the above sentence should be read as:
62 only provides path failover functionality, not load balancing over
63 the available paths etc.
64 Using suitable hardware like SCSI or FibreChannel disks it is
65 possible to have multiple (typically 2) host bus adapters access
66 the same physical disk drive.
68 Without a multipathing driver the
70 kernel would probe the disks multiple times, resulting in the creation of
73 entries for the same underlying physical device.
74 A unique label written in the GEOM label area allows
76 to detect multiple paths.
77 Using this information it creates a unique
83 device is subsequently used by the
85 kernel to access the disks.
86 Multiple physical access paths ensure that even in case of a path failure the
88 kernel can continue to access the data.
92 driver will disallow write operations to the underlying devices once the
93 fox device has been opened for writing.
98 needs a label on the disk as follows in order to work properly:
100 "0123456789abcdef0123456789abcdef"
101 "GEOM::FOX <--unique--id-->"
104 For the unique ID 16 bytes are available.
107 is the magic to mark a
111 The actual labelling is accomplished by
113 echo "GEOM::FOX someid" | dd of=/dev/da2 conv=sync
116 For FibreChannel devices it is suggested to use the Node World Wide
117 Name (Node WWN) as this is guaranteed by the FibreChannel standard to
119 The use of the Port WWN not recommended as each port of a given
120 device has a different WWN, thereby confusing things.
122 The Node WWN can be obtained from a verbose boot as in for example
124 isp1: Target 1 (Loop 0x1) Port ID 0xe8 (role Target) Arrived
125 Port WWN 0x21000004cfc8aca2
126 Node WWN 0x20000004cfc8aca2
129 This Node WWN would then be used like so:
131 echo "GEOM::FOX 20000004cfc8aca2" | dd of=/dev/da2 conv=sync
134 For non-FibreChannel devices you could for example use the serial
135 number of the device.
136 Regardless of what you use, make sure the label is unique.
138 Once the labelling has been performed and assuming the
140 module is loaded the kernel will inform you that it has found a new
142 device with a message similar to
144 Creating new fox (da2)
145 fox da2.fox lock 0xfffffc0000fdba20
149 To check which physical devices match a given
152 .Bd -literal -offset indent
157 Mediasize: 73407865344 (68G)
162 Mediasize: 73407865856 (68G)
166 Mediasize: 73407865856 (68G)
172 To check the status of the
177 Name Status Components
190 driver was written by
191 .An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .
192 This manual page was written by
193 .An Wilko Bulte Aq Mt wilko@FreeBSD.org .
197 driver depends on the underlying hardware drivers to do the right thing in case
199 If for example a hardware driver continues to retry forever,
201 is not able to re-initiate the I/O to an alternative physical path.
203 You have to be very sure to provide a unique label for each of the
206 Safety belts are not provided.
207 For FibreChannel devices it is suggested to use the Port WWN of the device.
208 The World Wide Name is guaranteed to be worldwide unique per the
209 FibreChannel standard.
213 framework has only seen light testing.
214 There definitely might be dragons here.
218 is completely obscure.
219 Just remember that any sly fox has multiple exits from its hole.
221 The examples provided are too FibreChannel-centric.